Industrial and Laboratory Nitrations

17 Low Temperature Process for TNT Manufacture Part 1. Laboratory Development MARION E. HILL, CLIFFORD L. COON, WILLIAM G. BLUCHER, GERALD J. McDONALD, CHESTER W. MARYNOWSKI, WESLEY TOLBERG, HOWARD M. PETERS, ROBERT L. SIMON and DONALD L. ROSS

Downloaded by UNIV OF AUCKLAND on May 3, 2015 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0022.ch017

Chemistry Laboratory, Stanford Research Institute, Menlo Park, Calif. 94025

Current processes for the manufacture of trinitrotoluene (TNT) produce atmospheric and water pollution that is only partly relieved by mechanical clean-up methods. TNT is currently produced from toluene by successive mono-, di-, and trinitrations with mixed aqueous n i t r i c and sulfuric acids in the f i r s t two steps and anhydrous mixed acid in the last. Each stage in the current process i s conducted at elevated temperatures, and side reactions in the overall process directly produce thousands of pounds of oxides of nitrogen, sulfuric acid aerosols, and volatile nitro organic products (such as tetranitromethane and nitroaromatics). These pollutants derive from the thermal decomposition of the aqueous n i t r i c acid solutions, from oxidative side reactions that produce as many as 40 by-product compounds, and from formation of unsymmetrical "meta" isomers. Since symmetrical TNT is inevitably accompanied by meta isomers as well as oxidation products, the crude material i s treated with sodium sulfite solutions to remove the undesirable isomers and nitroaromatics by derivatization. The spent sulfite solution, known as "red water," i s then disposed of by combustion to an inorganic ash, i t s e l f a disposal problem. We concluded that TNT production pollution could be a l l e viated by improving the chemical reactions that would obviate the decomposition of n i t r i c acid, the oxidative side reactions, and the formation of unsymmetrical isomers. The practical constraints were to achieve the technical solution by a process that was economical, proceeded rapidly and in high yields, and was applicable to large scale production. Voluminous literature reports aromatic nitration studies in various modes of mixed aqueous sulfuric and n i t r i c acids. The reported nitration media were consistently used under conditions that produced oxidation as well as nitration, with nitration

253

In Industrial and Laboratory Nitrations; Albright, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1976.

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INDUSTRIAL A N D LABORATORY

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being studied i n most d e t a i l (1). R e l a t i v e l y l i t t l e work had been reported on n i t r a t i o n i n the very strong a c i d systems that should be nonoxidative and heat s t a b l e . Consequently, we decided that l i t t l e could be gained by restudying methods s i m i l a r to those already reported and sought an e s s e n t i a l l y new approach that would take advantage of toluene r e a c t i v i t y and milder c o n d i t i o n s . In previous work, we had developed a n i t r a t i o n medium o f n i t r a t e s a l t s (such as sodium n i t r a t e and potassium n i t r a t e ) i n oleum that was s t a b l e at 140°C, h i g h l y r e a c t i v e , and nonoxidative on the substrate tribromodinitrobenzene (2). A p p l i c a t i o n of a s i m i l a r mixture to the n i t r a t i o n of toluene under mild c o n d i t i o n s revealed that d i n i t r o t o l u e n e was produced q u a n t i t a t i v e l y i n one step at room temperature. Subsequent work on e q u i v a l e n t anhydrous mixed a c i d systems produced s i m i l a r r e s u l t s at temperatures as low as -13°C. Only n i t r a t i o n of d i n i t r o t o l u e n e to TNT r e q u i r e d e l e vated temperatures and very strong a c i d . N i t r a t i o n of Toluene Anhydrous Mixed A c i d Systems. Although the i n i t i a l e x p e r i ments with n i t r a t e s a l t s produced q u a n t i t a t i v e y i e l d s of d i n i t r o toluene (DNT), there seemed to be no p r a c t i c a l way to r e c y c l e a c i d s or u t i l i z e the corresponding s u l f a t e s a l t by-products. This c o n s i d e r a t i o n l e d us to t r y a mixed a c i d system that was equival e n t to the s a l t mixtures i n nitronium i o n c o n c e n t r a t i o n . The mixed a c i d system was prepared e s s e n t i a l l y by dehydrating n i t r i c a c i d with oleum and producing nitronium b i s u l f a t e and s u l f u r i c acid: H H0N0

2

+ S0

SO 2

3

4

^N0 HS0 2

+ H S0

4

2

4

T h i s reagent i n 100% H S 0 d i n i t r a t e s toluene i n over 99% y i e l d as r a p i d l y as the reactants can be mixed, at temperatures between 0°C and the f r e e z i n g p o i n t of the n i t r a t i n g s o l u t i o n : 2

C H CH 6

5

3

+ 2 N0 HS0 2

4

4

. C H C H (N0 ) 3

6

3

2

+ 2H S0

2

2

4

DNT The d i n i t r a t i o n was n e a r l y q u a n t i t a t i v e under optimum condit i o n s but was appreciably i n f l u e n c e d by the mole r a t i o s of HN0 , S0 , and toluene. When s t o i c h i o m e t r i c or excess S0 was present, y i e l d s of DNT were lower probably because of s u l f o n a t i o n o f the r i n g . Best r e s u l t s were achieved with S0 s l i g h t l y l e s s than 3

3

3

3


17.

HILL

TNT Manufacture: Laboratory Development

ET AL.

stoichiometric

(Figure 1).

255

The medium produced by these concen-

t r a t i o n s was e s s e n t i a l l y N0 HS0 2

4

dissolved

i n anhydrous s u l f u r i c


acid.

Current methods f o r n i t r a t i n g toluene employ l a r g e excesses of n i t r i c acid i n aqueous media. Under the c o n d i t i o n s o f our experiments, however, only a s l i g h t excess of n i t r i c a c i d to toluene (2.1 to 1 or 2.2 t o 1) i s necessary to ensure DNT y i e l d s of 99%. As the r a t i o of n i t r i c a c i d to toluene i s increased to 4 to 1, the DNT y i e l d decreases s l i g h t l y to ~ 98%. The optimum molecular p r o p o r t i o n o f reagents f o r the DNT step was toluene, 1.00; HN0 , 2.11; and S 0 (as 20% oleum), 1.97; t h i s p r o p o r t i o n r e s u l t s i n a HN0 /toluene r a t i o of 2.11 and a S0 /HN0 r a t i o o f 0.93. The y i e l d o f DNT obtained at -10°C was 99.4%. 3

3

3

3

3

Because n i t r a t i o n i n a meta p o s i t i o n occurs almost e n t i r e l y i n the mononitration step, f a c t o r s that decrease meta n i t r a t i o n of toluene w i l l e v e n t u a l l y a f f e c t the f i n a l meta isomer content o f


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For example, n i t r a t i o n of e i t h e r pure o- or p - n i t r o t o l u e n e

to DNT

and then to TNT produced a product c o n t a i n i n g l e s s than

0.1% meta isomers.

T r i n i t r a t i o n o f pure 2,4-DNT gave no d e t e c t -

able meta-TNT isomers. The most e f f e c t i v e method f o r d e c r e a s i n g n i t r a t i o n i n the meta p o s i t i o n s of toluene i s to lower r e a c t i o n temperature.

Dini-

t r a t i o n s o f toluene c a r r i e d out a t 40°C or higher always give at l e a s t 3.5% meta isomers.

P o s i t i o n a l s e l e c t i v i t y toward l e s s meta

n i t r a t i o n i n c r e a s e s as the r e a c t i o n temperature i s lowered; at -10°C only 1.8% meta isomers are formed.

Lowering r e a c t i o n tem-


perature a l s o changes p o s i t i o n a l s e l e c t i v i t y i n favor of 2,4 2,6 n i t r a t i o n ;

f o r example, the 2,4/2,6 r a t i o a t -5°C was

while at -35°C t h i s r a t i o was 9.62. peratures r e s u l t i n s t i l l

over

6.27,

Although lower r e a c t i o n tem-

lower percentages of meta isomers, -10°C

appears to be the lower l i m i t f o r an economically f e a s i b l e process.

At -18°C f o r example, the o l e u m - n i t r i c a c i d mixture begins

to t h i c k e n and having a high v i s c o s i t y i t becomes i n c r e a s i n g l y d i f f i c u l t to maintain a w e l l - s t i r r e d , homogenous mixture.

Brine

s o l u t i o n s can be used f o r a -10°C r e a c t i o n temperature, but the costs a s s o c i a t e d with m a i n t a i n i n g lower temperatures become prohibitive. S o l u t i o n s of metal n i t r a t e s a l t s i n oleum are a l s o e f f e c t i v e n i t r a t i n g media f o r converting toluene t o DNT,

but they are

n e i t h e r as economical nor as convenient as the anhydrous s u l f u r i e a c i d mixture.

nitric-

The a c t i v e n i t r a t i n g agent f o r the n i t r a t e

s a l t s o l u t i o n i s probably N0 HS0 , j u s t as i n the n i t r i c - s u l f u r i c 2

acid

4

system.

MN0

3

+ S0

+ H S0

3

2

H„S0„ 2 4—^ Q HS0 N

4

2

+ MHS0

4

4

The n i t r a t i n g s o l u t i o n s were prepared by s a t u r a t i n g 15% fuming H S0 2

w i t h the metal n i t r a t e at ambient

4

temperatures.

However,

the s a l t s were not s o l u b l e enough to r e a c t with a l l the S0 H S 0 ) according to the above equation. 2

2

7

Consequently, S 0

(as

3

3

present to compete as a r e a c t a n t with the n i t r a t i n g agent. n i t r a t i n g s o l u t i o n s prepared from NaN0 and 5.7% S0 ; w i t h KN0 3

free S0 . 3

3

3

contained 14.2% N0 HS0 2

there was 20.2% N0 HS0 2

4

and only

Both systems r e a d i l y n i t r a t e d toluene to DNT

i n 97% y i e l d with KN0

3

and i n 88% y i e l d with NaN0 .

y i e l d s obtained with the KN0

3

3

was The 4

1.5% a t -10°C,

The h i g h e r

system were a t t r i b u t e d to the lower

concentration of S0 . 3

Aqueous Mixed A c i d Systems. Although anhydrous systems appear to be optimum, e x c e l l e n t d i n i t r a t i o n r e s u l t s were obtained


17.

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TNT

Manufacture:

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257

Development

i n media composed of n i t r i c and s u l f u r i c a c i d s and up to 7% water ( 3 ) . These mixtures are e q u a l l y as e f f e c t i v e as the oleumn i t r i c a c i d mixtures i n converting toluene to DNT i n y i e l d s greater than 99% i n 1 nr. The decrease i n n i t r a t i o n i n the meta p o s i t i o n s showed the normal r e a c t i o n temperature dependence and ranged from 2.06% at -5°C to 1.40% at -35°C, as shown i n Table I. The temperature dependence f o r p o s i t i o n a l s e l e c t i v i t y of 2,4over 2,6-DNT follows the same trend as i n the anhydrous systems.


Table I TEMPERATURE DEPENDENCE OF ISOMER DISTRIBUTION AND SET POINT OF THE DIΝITROTOLUENE PRODUCT DNT

Reaction Temp., °C -5 -15 -25 -35

84.48 85.34 85.47 88.98

Isomers, %

2,6-

3,4-

13.46 12.83 11.77 9.62

1.41 1.29 1.26 1.07

2,3 - +

2,5-

Total Meta, % 2.06 1.82 1.76 1.40

0.65 0.53 0.50 0.33

" H S0 /HN0 /H 0 weight r a t i o , 90.6/6.3/3.1; HN0 /toluene 4/1. 2

4

3

2

3

Set

Pt„ °C

61.0 61.8 62.5 63.7

ratio,

When water c o n c e n t r a t i o n s were allowed to exceed 7%, the r e a c t i o n r a t e was considerably reduced, and complete d i n i t r a t i o n was not obtained at low r e a c t i o n temperatures. The DNT was ac companied by mononitrotoluenes (MNT) i n v a r y i n g r a t i o s , depending on the amount of water present. At a s u l f u r i c a c i d c o n c e n t r a t i o n of 80%, i t was not p o s s i b l e to l i m i t the r e a c t i o n to mononitrat i o n except at low temperatures. At 70% s u l f u r i c a c i d concentra t i o n , d i n i t r a t i o n and mononitration occurred u n l e s s the n i t r i c a c i d c o n c e n t r a t i o n was held to 5% or l e s s . At s u l f u r i c a c i d con c e n t r a t i o n s between 40% and 60% mononitration was r e a d i l y achieved, and very l i t t l e d i n i t r a t i o n occurred. Even at low temperature, however, aqueous n i t r a t i o n media produce more meta s u b s t i t u t i o n . The amount formed depends more on water c o n c e n t r a t i o n than on e i t h e r s u l f u r i c o r n i t r i c a c i d con c e n t r a t i o n s . At a constant water concentration, v a r i a t i o n s i n the s u l f u r i c / n i t r i c a c i d r a t i o s r e s u l t i n l i t t l e change i n meta isomer formation. In a l l aqueous media experiments, the meta isomers ranged between 3% and 5% i n the isomer d i s t r i b u t i o n . We can con clude therefore that c o n d i t i o n s s u f f i c i e n t f o r mononitration (as


INDUSTRIAL AND

258

LABORATORY

NITRATIONS


i n current p l a n t s ) but not f o r d i n i t r a t i o n are a l s o c o n d i t i o n s f o r high meta formation; a c i d strengths s u f f i c i e n t f o r d i n i t r a t i o n reduce meta concentrations. Nitronium Trifluorornethanesulfonate. Another i n t e r e s t i n g method f o r the p r e p a r a t i o n of e i t h e r MNT or DNT from toluene i s the use of t r i f l u o r o m e t h a n e s u l f o n i c a c i d (TFSA) and n i t r i c a c i d (4,5,6). The main i n t e r e s t i n t h i s medium i s i t s a b i l i t y to n i t r a t e at extremely low temperatures to products that contain very low concentrations of meta isomers. Two equivalents of TFSA and one of anhydrous n i t r i c a c i d com bine to form a white c r y s t a l l i n e s o l i d . T h i s r e a c t i o n can be c a r r i e d out between the neat r e a c t a n t s or i n solvents such as CH C1 , CC1 , H S 0 , or excess TFSA i t s e l f . The s o l i d i s very hygroscopic, melts at 60-65°C, and p a r t i a l l y sublimes at 60-70°C (1-2 mm). Elemental a n a l y s i s and Raman spectroscopy showed i t to be a mixture of nitronium t r i f l u o r o m e t h a n e s u i f o n a t e (NTFS) and hydronium trifluoromethanesuifonate; s t r u c t u r e assignment was con firmed i n l a t e r work by Effenberger and Geke (6). 2

2

4

2

4

2CF S0 H + HNO3 3

+

+

^N0 CF S0 " + H 0 CF S0 "

3

2

3

3

3

3

3

Nitronium t r i f l u o r o m e t h a n e s u l f o n a t e proved to have e x c e l l e n t n i t r a t i n g p r o p e r t i e s i n each r e a c t i o n medium i n v e s t i g a t e d . ArH + x N 0 C F S 0 2

3

3

^ΑΓ(Ν0 ) 2

+ xCF S0 H

χ

3

3

Product y i e l d s were nearly q u a n t i t a t i v e i n r e a c t i o n times of 1 to 60 minutes i n a v a r i e t y of solvents i n c l u d i n g s u l f u r i c a c i d , TFSA, aqueous TFSA, methylene c h l o r i d e , and CFC1 , thus i n d i c a t i n g the absence of s i d e r e a c t i o n s . In s u l f u r i c a c i d or mixtures o f s u l f u r i c a c i d and TFSA, d i n i t r a t i o n of toluene by the nitronium s a l t gave high y i e l d s of DNT. In aqueous TFSA, as i n aqueous s u l f u r i c a c i d , e i t h e r mono- or d i n i t r a t i o n could be made to occur depend i n g on the concentration of the a c i d . Although i t i s not s u r p r i s i n g that NTFS i s an e f f e c t i v e n i t r a t i n g reagent i n s u l f u r i c a c i d , TFSA, or aqueous s o l u t i o n s of these a c i d s , i t has a l s o proved to be an e x c e p t i o n a l l y good n i t r a t i n g system i n i n e r t organic s o l v e n t s . In organic s o l v e n t s , mono- or d i n i t r a t i o n of toluene can be c o n t r o l l e d by r e a c t i o n temperature. At -110° to -60°C i n methylene c h l o r i d e , mononitrat i o n was accompanied by only a trace of DNT products; at 0°C, or higher, q u a n t i t a t i v e y i e l d s of DNT were obtained. At -30°C mix tures of MNT and DNT were formed. NTFS, needed i n only s l i g h t 3


HILL E T AL.


17.

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Manufacture:

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Development

259

s t o i c h o i m e t r i c excess, proved to be only s l i g h t l y l e s s e f f e c t i v e i n carbon t e t r a c h l o r i d e and pentane at 0°C and below. The mononitration of toluene i s very f a s t i n a l l solvent systems, o c c u r r i n g w i t h i n one minute at -110°C to -60°C; but d i n i t r a t i o n at 0°C i s somewhat slower, r e q u i r i n g about 30 min f o r completion. Although our r e s u l t s show that NTFS n i t r a t i o n r a t e s are not as f a s t i n an i n e r t solvent as they are i n n i t r i c a c i d / oleum systems, NTFS i s a very strong n i t r a t i n g system and one of the few that w i l l convert toluene to DNT at 0°C. NTFS shows a high degree of p o s i t i o n a l s e l e c t i v i t y as a reagent f o r aromatic n i t r a t i o n . As with a l l other n i t r a t i n g systems the amount of meta isomer produced i n toluene n i t r a t i o n depends d i r e c t l y on r e a c t i o n temperature. At -60°, -90°, and -110°C i t s r e a c t i o n with toluene gives MNT that contains 0.53%, 0.36%, and 0.23% m-MNT, r e s p e c t i v e l y . The l a s t value i s the lowest that has been r e l i a b l y recorded f o r an MNT s y n t h e s i s . Since most meta s u b s t i t u t i o n takes place i n the mononitration stage, the f i n a l meta isomer content i n DNT can be g r e a t l y i n f l u e n c e d by running the mononitration step a t low temperatures followed by d i n i t r a t i o n at 0-25°C. Thus, when mononitration was c a r r i e d out at -110°, -90°, -60°, -30°, 0°, and 25°C, followed by d i n i t r a t i o n at 0° or 25°C, the r e s u l t i n g DNT products contained 0.33%, 0.51%, 0.75%, 1.08%, 1.33%, and 1.72% meta isomers, r e s p e c t i v e l y . The 0.33% value i s the lowest that has been r e l i a b l y recorded f o r meta isomers i n a DNT s y n t h e s i s . N i t r a t i o n of D i n i t r o t o l u e n e The use of anhydrous mixed a c i d systems f o r low temperature d i n i t r a t i o n of toluene l e d us to choose the same type of system f o r t r i n i t r a t i o n since i n a p l a n t operation no e s s e n t i a l change of n i t r a t i o n system would be necessary. Work on the t r i n i t r a t i o n step began with c o n s i d e r a t i o n of the appropriate concentration of oleum to be used and methods of ensuring r e p r o d u c i b l e r e a c t i o n c o n d i t i o n s . The choice of the S0 concentration determines the concentration of N0 HS0 , and at l e a s t two f a c t o r s favor a high concentration of the n i t r a t i n g agent f o r a manufacturing process: (1) the r e a c t i o n r a t e , and thus the o v e r a l l p l a n t production r a t e , i s a f u n c t i o n of the N0 HS0 concentration and (2) the r e a c t o r volume and number of r e a c t o r s r e q u i r e d to produce TNT at a s p e c i f i e d r a t e are determined i n p a r t by the concentration of the n i t r a t i n g agent. These f a c t o r s must be weighed against s a f e t y c o n s i d e r a t i o n s because we 3

2

2

4

4


260


NITRATIONS

have found that too high a concentration of r e a c t a n t s sometimes leads to runaway r e a c t i o n s . High concentrations o f S 0 i n s u l f u r i c a c i d were d e l e t e r i o u s to c o n t r o l o f n i t r a t i o n although high concentrations o f n i t r a t i n g agent were p o s s i b l e . Rapid decomposition o f s t a r t i n g m a t e r i a l r e s u l t e d from heat produced by t r i n i t r a t i o n with n i t r i c a c i d i n 65% and 40% oleum. Equimolar amounts o f HN0 and S 0 i n 30% oleum produced a maximum temperature o f 130°C and r e s u l t e d i n a 94.0% y i e l d o f TNT. When S 0 i n 10% excess was used to prepare the N0 HS0 , the temperature reached 97°C and the y i e l d o f TNT was 95.0%. 3

3

3

3


2

4

To t e s t more c a r e f u l l y the e f f e c t o f the S0 /HN0 r a t i o on the y i e l d of TNT, i t was necessary to e l i m i n a t e temperature as a v a r i a b l e . The mixed a c i d s o l u t i o n was heated i n an o i l bath a t 90°C, and DNT was added i n small p o r t i o n s so that the r e a c t i o n mixture was maintained a t 91-92°C by the heat o f r e a c t i o n . Essent i a l l y no e f f e c t was seen as the S0 /HN0 r a t i o was v a r i e d i n the range from 0.9 to 1.0 to 1.1; y i e l d s o f 94% were obtained. 3

3

3

3

An i n v e s t i g a t i o n i n t o the nature o f the s i d e r e a c t i o n s that l i m i t the TNT y i e l d to about 94% i n d i c a t e d that DNT undergoes competitive n i t r a t i o n and o x i d a t i o n r e a c t i o n s i n accordance with the f o l l o w i n g scheme:

TNT

——-Oxidation

products

Gaseous o x i d a t i o n products

S u l f o n a t i o n was e l i m i n a t e d as a p o s s i b l e side r e a c t i o n by an experiment i n which DNT was t r e a t e d w i t h 15% fuming H S 0 a t 90°C; 99% DNT was recovered. T r i n i t r o b e n z o i c a c i d was e s t a b l i s h e d as one o f the byproducts o f TNT o x i d a t i o n . Although present i n minor amounts, i t was obtained as the p r i n c i p a l c o n s t i t u e n t of a t l e a s t f i v e compounds i s o l a t e d . To determine whether the major l o s s was due to o x i d a t i o n of DNT or TNT, we tested the s t a b i l i t y o f TNT to the n i t r a t i o n c o n d i t i o n s ; 98.6% TNT was recovered. 2

4

I n f r a r e d a n a l y s i s o f samples o f the gas phase over a t r i n i t r a t i o n r e a c t i o n confirmed the presence o f gaseous by-products; strong i n f r a r e d bands f o r C 0 , CO, and N 0 were observed. Since no more than 1.4% o f the TNT undergoes o x i d a t i v e decomposition, and s i n c e some o f the TNT by-products are ( a t l e a s t p a r t l y ) s o l i d s , 2

2


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the major p r o p o r t i o n of the gaseous by-products must a r i s e from o x i d a t i o n o f DNT and account f o r about 5% o f the m a t e r i a l balance. I t i s obvious that the major source o f l o s s i s by o x i d a t i o n o f DNT. To optimize t r i n i t r a t i o n under useable c o n d i t i o n s , we chose 1 hr as the maximum time f o r completion of the r e a c t i o n . We chose a l s o to i n i t i a t e the r e a c t i o n a t higher temperatures to avoid an exotherm that occurs when heating from ambient to the d e s i r e d n i t r a t i o n temperature. The r e a c t i o n times r e q u i r e d f o r complete r e a c t i o n , when the r a t i o of reagents was 3 moles o f N0 HS0 (prepared from HN0 and 30% oleum) per mole o f DNT, were 140 min a t 70°C, 100 min a t 80°C, and 50 min a t 90°C. The r e a c t i o n could be completed w i t h i n 60 min by h e a t i n g f o r 30 min a t 70°C, followed by 15 min each a t 80° and 90°C. I n i t i a t i n g the r e a c t i o n a t 70°C, where the r a t e i s much slower than a t 90°C, makes i t e a s i e r to c o n t r o l the temperature; the elevated temperatures are then used to complete the r e a c t i o n a f t e r much o f the i n i t i a l DNT charge has been consumed. 2


TNT

4

3

Although the t r i n i t r a t i o n of DNT could be conducted i n high y i e l d and o x i d a t i o n products were p r i m a r i l y gases, the corresponding i n o r g a n i c r e d u c t i o n by-product was n i t r o s y l s u l f u r i c a c i d . The presence o f N0HS0 meant that the n i t r a t i n g medium would r e quire clean-up a t some stage i n the r e c y c l e o f spent a c i d s , a l though i n nine consecutive n i t r a t i o n s o f toluene t o TNT w i t h r e f o r t i f i e d used a c i d , l i t t l e e f f e c t by i t s presence was observed. Consequently, s e v e r a l attempts were made to prevent DNT o x i d a t i o n by (a) using o x i d a t i o n i n h i b i t o r s , (b) i n c r e a s i n g the concentrat i o n o f N0 HS0 while lowering the r e a c t i o n temperature, (c) i n c r e a s i n g the S 0 c o n c e n t r a t i o n , and (d) temperature programming the optimum n i t r a t i o n concentrations. An extensive study of the l a s t procedure showed that n i t r a t i o n of DNT a t 40°C proceeds a t an a p p r e c i a b l e r a t e and i s accompanied by o x i d a t i o n o f the DNT to gaseous products. Higher temperatures, e i t h e r programmed from 40° to 90°C or i s o t h e r m a l l y a t 90°C, cause only a v a r i a t i o n i n n i t r a t i o n r a t e s and l i t t l e v a r i a t i o n i n o x i d a t i o n r a t e s . Reactions a t the higher temperatures a l s o produce tetranitromethane (TNM) as w e l l as CO, C 0 , N 0, and N0 . Comparative n i t r a t i o n experiments of a l l the DNT isomers except 3,5-DNT show r a t e s from f a s t e s t to slowest i n the order 2,6- > 3,4- > 2,4- BÏ 2,52,3-DNT; a l l isomers undergo o x i d a t i o n . 4

2

4

3

2

2

2

A d e t a i l e d k i n e t i c study o f n i t r a t i o n / o x i d a t i o n of three DNT isomers, by D. S. Ross and N. Kirshen, i s described elsewhere i n t h i s symposium.



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NITRATIONS

The n i t r a t i o n o f 3,4-DNT a t a r a t e f a s t e r than 2,4-DNT i s unexpected and cannot be explained s o l e l y by d i r e c t i v e e f f e c t c o n s i d e r a t i o n s proposed by other workers (7). I n t r o d u c t i o n o f an e n t e r i n g group on the toluene nucleus i s a f f e c t e d not only by the o r i e n t a t i o n o f the methyl and n i t r o groups already present but a l s o by s t e r i c , temperature, and concentration f a c t o r s . In the three meta isomers studied, two n i t r o groups are adjacent. One group i s out o f the plane o f the r i n g and thus e x e r t s l i t t l e d i r e c t i n g e f f e c t toward n i t r a t i o n . For example, i n 2,3-DNT the 2 - n i t r o group i s most probably out o f plane, l e a v i n g the methyl and 3 - n i t r o groups opposing each other i n d i r e c t i n g f u r t h e r n i t r a t i o n . Conversely, i n 2,4-DNT both n i t r o groups are i n plane with the r i n g and thus exert d e a c t i v a t i n g e f f e c t s . The methyl and 2- n i t r o groups d i r e c t n i t r a t i o n to the 4- and 6- p o s i t i o n s ; however, i n 2,5-DNT these e f f e c t s are counteracted by the 5 - n i t r o group, which d i r e c t s n i t r a t i o n to the 3 - p b s i t i o n . The f a s t e r n i t r a t i o n r a t e shown by 3,4-DNT i n d i c a t e s that the 3- n i t r o group o f 3,4-DNT i s the one most probably out o f plane, l e a v i n g the methyl and 4 - n i t r o groups to d i r e c t n i t r a t i o n . Because the out-of-plane c o n f i g u r a t i o n makes 3,4-DNT s i m i l a r to that of p - n i t r o t o l u e n e , i t s n i t r a t i o n r a t e i s f a s t e r than that o f the other DNT meta isomers, as w e l l as 2,4-DNT. T h i s p o s t u l a t i o n i s i n l i n e with the r e s u l t s obtained from our study on the n i t r a t i o n r a t e s o f 2,4- and 2,6-DNT. Because the p r o b a b i l i t y o f a n i t r o group being out o f plane i s g r e a t e r i n 2,6-DNT and because i t s 4 - p o s i t i o n i s l e s s s t e r i c a l l y hindered, t h i s isomer should n i t r a t e f a s t e r than 2,4-DNT, as shown by our r e s u l t s . TNT

Isolation

The requirement f o r a process adaptable to p l a n t o p e r a t i o n made product i s o l a t i o n very c r i t i c a l . Because o f the high a c i d s t r e n g t h and s o l u b i l i t y o f TNT i n the a c i d medium, e f f i c i e n t c r y s t a l l i z a t i o n o f TNT a t lower temperatures was necessary f o r r e c y c l e o f the spent a c i d s . In a t y p i c a l t r i n i t r a t i o n r e a c t i o n with pure 2,4-DNT, the product TNT was f i l t e r e d from the n i t r a t i o n medium a t 0°C, and again a t -10°C. About 79% o f the TNT produced i n the r e a c t i o n c r y s t a l l i z e d from s o l u t i o n . The composition of the wet product was 70% TNT and 30% a c i d . A f t e r washing and d r y i n g , t h i s TNT had a s e t p o i n t of 80.6°C, showing that the i s o l a t i o n and p u r i f i c a t i o n technique gives a pure product when 2,4-DNT i s used as s t a r t i n g m a t e r i a l .



17.

HILL E T A L .

TNT

Manufacture:

Laboratory

Development

263

The amount o f a c i d occluded by the c r y s t a l s was s u b s t a n t i a l l y i n f l u e n c e d by the s i z e o f the c r y s t a l s . A slow r a t e o f c r y s t a l growth, beginning while the s o l u t i o n was s t i l l q u i t e warm, gave l a r g e c r y s t a l s ; the occluded a c i d amounted to about 30% to 35% o f the t o t a l weight o f the wet c r y s t a l s or about 43% to 54% o f the dry weight of the TNT. On the other hand, i f extensive o i l i n g occurred as the TNT s o l u t i o n cooled, very r a p i d c r y s t a l l i z a t i o n took place, g i v i n g small c r y s t a l s that were very d i f f i c u l t t o f i l t e r and occluded a l a r g e amount of a c i d . In one such case, the a c i d amounted to 53% o f the t o t a l weight o f the wet c r y s t a l s . In t r i n i t r a t i o n of mixed DNT isomers t y p i c a l o f a c t u a l condit i o n s , l e s s than 79% o f the TNT c r y s t a l l i z e s out o f the mixed a c i d s . A value of 70% i s more n e a r l y r e p r e s e n t a t i v e o f a c t u a l c o n d i t i o n s . The remainder i s r e c y c l e d through the process with the a c i d f i l t r a t e . Scale-up to M i n i p l a n t A m i n i p l a n t was constructed f o l l o w i n g the schematic diagram of F i g u r e 2 that had a c a p a c i t y o f 2 pounds per hour when operated i n a continuous mode. The p r i n c i p a l steps, however, were most emphasized i n p r i m a r i l y an e x p l o r a t o r y batch study.

HN0

TOLUENE

DINITRATOR

3

+ S0

3

TRINITRATORS

80%

TNT TO ' WORKUP

20%

NITRATING ACID

DNT RECYCLE ACIDS

SOLVENT. EXTRACTION SURPLUS H S0 2

4

TO ACID RECOVERY

Figure 2.

Process based on

HNO /SO /H S0 s

s

s

4



264

Toluene and r e c y c l e d mother l i q u o r from the t r i n i t r a t i o n step were precooled to about -10°C and allowed to r e a c t a t that temperature i n a s t r o n g l y a g i t a t e d , w e l l - c o o l e d , multistage turbo-reactor intended to operate i n plug flow mode with toluene apportioned e q u a l l y among the s e v e r a l stages. The toluene was r a p i d l y d i n i t r a t e d by a s t o i c h i o m e t r i c amount o f N0 HS0 with concurrent formation o f H S 0 , the p r i n c i p a l by-product o f the process. Thus, the e f f l u e n t from the d i n i t r a t o r i s a mixture of DNT and r e c y c l e d TNT d i s s o l v e d i n H S 0 . The y i e l d s and condit i o n s of the l a b o r a t o r y study were e s s e n t i a l l y confirmed; DNT was obtained i n 97% to 98% y i e l d s with meta isomer content of 2.2 to 2.3%. 2

2

4

4

2


NITRATIONS

4

P a r t o f the e f f l u e n t was allowed to flow d i r e c t l y to an a c i d f o r t i f i c a t i o n tank, where f r e s h S 0 and HN0 were added to b r i n g the c o n c e n t r a t i o n of N0 HS0 to the r e q u i r e d l e v e l f o r the subsequent t r i n i t r a t i o n r e a c t i o n . However, a p o r t i o n o f the d i n i t r a t o r e f f l u e n t was f i r s t d i v e r t e d and the by-product H S 0 separated by methylene c h l o r i d e e x t r a c t i o n of the DNT with a Pyrex multistage counter current e x t r a c t i o n column. Good e x t r a c t i o n and separation of solvent were achieved. A f t e r the methylene c h l o r i d e was subsequently s t r i p p e d out and r e c y c l e d , the e x t r a c t e d DNT and TNT was j o i n e d to the undiverted d i n i t r a t o r e f f l u e n t stream e n t e r i n g the a c i d f o r t i f i c a t i o n tank. From the a c i d f o r t i f i c a t i o n tank, the d i n i t r a t i o n products and the f o r t i f i e d acids flowed i n succession through three s t i r r e d t r i n i t r a t i o n r e a c t o r s maintained a t about 80°, 85°, and 90°C. The overflow from the t h i r d t r i n i t r a t o r c o n s i s t e d e s s e n t i a l l y o f TNT d i s s o l v e d i n a c i d s . The TNT was c r y s t a l l i z e d by c o o l i n g the l i q u o r s i n a three-stage upflow, i n c l i n e d scraped pipe c r y s t a l l i z er, and then f i l t e r e d and dropped i n t o a r e c e i v e r c o n t a i n i n g 70% H S 0 , which served as the f i r s t wash f o r the TNT product. 3

2

3

4

2

2

4

4

In general, the chemical performance data were comparable to the l a b o r a t o r y r e s u l t s . For example, the o v e r a l l TNT y i e l d from one c y c l e of d i n i t r a t i o n plus t r i n i t r a t i o n was 91.1% based on toluene and 74.3% based on n i t r i c a c i d . These values may be compared with the average l a b o r a t o r y values o f 93% and 75%, respectively. Summary Methods were developed f o r the improved s y n t h e s i s o f TNT to a l l e v i a t e p o l l u t i o n problems a s s o c i a t e d with c u r r e n t manufacturing processes. A comparison o f many n i t r a t i o n methods showed that modified o l e u m - n i t r i c a c i d mixtures were the most e f f e c t i v e at


17.

HILL E T A L .

TNT

Manufacture:

Laboratory

Development

265


g i v i n g high y i e l d s of TNT while e m i t t i n g l i t t l e or no atmospheric p o l l u t a n t s . Conducting toluene d i n i t r a t i o n at low temperature (-10°C) e l i m i n a t e s o x i d a t i o n and reduces the amount of the unde s i r a b l e meta isomers formed to 1-2% i n c o n t r a s t to ca. 4% i n con v e n t i o n a l processes. Consequently, "red water" problems a s s o c i a ted with TNT p u r i f i c a t i o n by t r e a t i n g crude product with sodium s u l f i t e could be s u b s t a n t i a l l y diminished. Thus, a two-stage n i t r a t i o n system was developed i n which toluene i s d i n i t r a t e d i n 99% y i e l d at -10°C u s i n g an o l e u m - n i t r i c a c i d mixture, followed by t r i n i t r a t i o n o f the DNT i n anhydrous n i t r i c / s u l f u r i c a c i d at 90°C i n 94% y i e l d . A procedure f o r the recovery and r e c y c l e of a l l a c i d s was developed, and the o v e r a l l process was confirmed i n a m i n i p l a n t scale-up. Other r e s e a r c h has shown that DNT can be prepared r a p i d l y and i n high y i e l d u s i n g anhydrous n i t r a t e s a l t / s u l f u r i c a c i d or n i t r i c / s u l f u r i c a c i d mix tures c o n t a i n i n g 0-7 wt% water. Meta isomer percentages are l e s s than 2% when r e a c t i o n temperatures are -10°C or lower. A unique n i t r a t i n g system was a l s o developed c o n s i s t i n g of t r i f l u o r o m e t h a n e s u l f o n i c a c i d and n i t r i c a c i d i n an organic solvent at -110° to 30°C. T h i s system produced mono or d i n i t r o t o l u e n e i n high y i e l d s and with l e s s than 0.5% meta isomer content. Acknowledgment The authors s i n c e r e l y a p p r e c i a t e the support given us by the P i c a t i n n y Arsenal and Army M a t e r i e l Command and p a r t i c u l a r l y the v a l u a b l e c o n t r i b u t i o n s and continued encouragement provided throughout t h i s study by many i n d i v i d u a l s of these o r g a n i z a t i o n s .

Appendix EXPERIMENTAL PROCEDURES General Elemental analyses were determined by the Stanford Univer s i t y M i c r o a n a l y t i c a l Laboratory. I n f r a r e d spectra were run on a Perkin-Elmer 237 spectrophotometer and Raman spectra on a Specs Ramalog 1401 Double Monochromator, Coherent R a d i a t i o n Model 52, Mixed Gas Argon Krypton L a s e r . Gc analyses were run on an Aero graph 1520 gas chromatograph equipped with a flame i o n i z a t i o n d e t e c t o r . Mononitrotoluene mixtures were analyzed on a 12 f t χ 0.125 i n . , 4% QF-1 on 100/120 mesh Chromosorb G, acid-washed, DMCS-treated column. D i n i t r o t o l u e n e and n i t r o b e n z o t r i f l u o r i d e


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mixtures were analyzed on a 12 f t χ 0.125 i n . column packed with 4% poly-m-phenyl ether ( s i x r i n g ) on 80/100 mesh Chromosorb G, acid-washed, DMCS-treated. B a s e l i n e s e p a r a t i o n of a l l DNT i s o mers was obtained except f o r the 2,3 and 2,5 isomers, which had the same r e t e n t i o n time. A 10 f t χ 0.125 i n . 25% s i l i c o n e o i l on 100/120 mesh Chromosorb G, acid-washed, DMCS-treated column gave complete b a s e l i n e separation of the s i x TNT isomers. Each a n a l y s i s was compared with that of a standard that contained approximately the same isomer d i s t r i b u t i o n .


Starting Materials Commercial grade toluene was d i s t i l l e d before use to o b t a i n f r a c t i o n s that were pure by gc a n a l y s i s . T r i f l u o r o m e t h a n e s u l f o n i c a c i d , obtained from The 3M Company under the name of t r i m s y l a t e a c i d (FC-24), was analyzed as 99% pure by p r e p a r a t i o n of i t s a n i l i n e s a l t and was used without f u r t h e r p u r i f i c a t i o n . D i n i t r a t i o n of Toluene with N i t r i c A c i d i n Oleum The f o l l o w i n g procedure i s r e p r e s e n t a t i v e of the method used to determine general r e a c t i o n r a t e s and to study the e f f e c t of temperature on the d i n i t r a t i o n of toluene i n oleum/HN0 mixtures. Absolute HN0 (16.2 g, 257 mmole) was added dropwise to 93.5 g (ca. 50 ml) of 20.6% oleum (240 mmole of S0 ) using exter nal c o o l i n g to maintain a temperature of 20° to 30°C. The s o l u t i o n was prepared i n a 100-ml three-necked round-bottom f l a s k f i t t e d with a mechanical s t i r r e r , thermometer, and pressuree q u a l i z i n g dropping funnel with d r y i n g tube attached. The drop ping funnel was then r e p l a c e d with a second one c o n t a i n i n g 11.3 g of neat toluene. The N0 HS0 s o l u t i o n was cooled i n a s a l t - i c e bath, and toluene (11.2 g, 122 mmole) was added slowly over 45 min a t -6° to -9°C. A f t e r an a d d i t i o n a l 15 min, the s o l u t i o n was quenched i n 325 g of i c e . The product was e x t r a c t e d with methy lene c h l o r i d e , washed with saturated NaCl s o l u t i o n , d r i e d over MgS0 , and evaporated to dryness with a r o t a r y evaporator. The s o l i d was d r i e d to constant weight under vacuum over Κ0Η p e l l e t s ; 22.1 g (99.4%) of DNT was obtained. T h i s product was analyzed by gc and found to c o n t a i n 15.6% 2,6-DNT, 0.6% 2,3-DNT and 2,5-DNT, 82.6% 2,4-DNT, and 1.2% 3,4-DNT. 3

3

3

2

4

4

D i n i t r a t i o n of Toluene with Sodium N i t r a t e i n Fuming S u l f u r i c A c i d A p r e l i m i n a r y experiment e s t a b l i s h e d the s o l u b i l i t y of NaN0 i n 15% fuming H S 0 as 0.176 g/ml a t ambient temperature. Dry 2

4


3

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HILL E T A L .

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Manufacture:

Laboratory

Development

267

NaN0 (10.74 g, 127 mmole) was placed i n a 100-ml f l a s k equipped with a mechanical s t i r r e r , thermometer, and graduated a d d i t i o n funnel with a d r y i n g tube attached. The system was flushed with dry n i t r o g e n and 61 ml of 15% fuming H S 0 (217 mmole o f S 0 ) was added from the funnel, keeping the mixture a t 0°C by e x t e r n a l c o o l i n g . A f t e r the NaN0 had d i s s o l v e d , the s o l u t i o n was cooled to -15°C and toluene (2.80 g, 30.4 mmole) was added dropwise with vigorous s t i r r i n g over 1 hr while keeping the temperature below -10°C. A f t e r 15 min the s o l u t i o n was poured i n t o 300 g of i c e and the product extracted with methylene c h l o r i d e . The e x t r a c t was d r i e d over C a C l and the solvent removed with a r o t a r y evaporator; 4.88 g (88.3%) of DNT was obtained. 3

2

4

3

3


2

D i n i t r a t i o n of Toluene with Potassium N i t r a t e i n Fuming S u l f u r i c Acid The s o l u b i l i t y of KN0 i n 15% fuming H S 0 was determined as 0.317 g/ml. Dry KN0 (7.30 g, 72.2 mmole) was d i s s o l v e d i n 23 ml of 15% fuming H S 0 (81.9 mmole o f S 0 ) as above. Toluene (2.11 g, 22.9 mmole) was added dropwise a t -10°C over 15 min. A f t e r an a d d i t i o n a l 15 min, the r e a c t i o n mixture was quenched i n 300 g of i c e and worked up as above; 4.05 g (97.2%) o f DNT was obtained. 3

2

4

3

2

4

3

P r e p a r a t i o n o f DNT with Mixed Aqueous A c i d s A n i t r a t i n g mixture was prepared from 280 g 96% H S 0 and 27 g 70% HN0 (0.300 mole) to g i v e a c l e a r , c o l o r l e s s s o l u t i o n c o n t a i n i n g by weight 87.56% H S 0 , 6.16% HN0 , and 6.29% H 0. To the s l u r r y that r e s u l t s when t h i s s o l u t i o n i s cooled to -35°C there was added 13.10 g o f toluene (0.142 mole) over 20 min. The mixture was then s t i r r e d a t -35°C f o r 1 hour and f i n a l l y quenched by pouring onto 250 g o f i c e . The product was separated by ext r a c t i o n with seven 25-ml p o r t i o n s o f methylene c h l o r i d e . These were combined, d r i e d (MgS0 ), and the solvent removed under vacuum to g i v e 25.73 g of DNT (99.5% y i e l d ) . Gc a n a l y s i s o f t h i s product showed that i t contained 11.13% 2,6-DNT, 0.30% 2,3- and 2,5DNT, 87.45% 2,4-DNT, and 1.12% 3,4-DNT. T o t a l meta isomers were 1.43%. 2

4

3

2

4

3

2

4

P r e p a r a t i o n of MNT with Nitronium Trifluoromethanesulfonate A s o l u t i o n c o n t a i n i n g 6 g (40 mmol) o f t r i f l u o r o m e t h a n e s u l f o n i c a c i d d i s s o l v e d i n 100 ml o f C H C 1 was placed i n a 200-ml f l a s k equipped with a mechanical s t i r r e r , a d d i t i o n funnel, and 2

2


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thermometer. A 1.26-g sample (20 mmol) of anhydrous HN0 was added to t h i s s o l u t i o n , causing a white, c r y s t a l l i n e s o l i d to separate from s o l u t i o n . The temperature of the mixture was lower ed to -60°C by a dry ice-acetone bath, and 0.46 g (5 mmol) of toluene was added i n one p o r t i o n . The mixture was s t i r r e d at -60°C f o r 1 hr and then q u i c k l y poured onto 100 g of crushed i c e . The r e s u l t i n g mixture was e x t r a c t e d with three 100-ml p o r t i o n s of CH C1 . These were combined and d r i e d (MgS0 ), and the s o l v e n t was removed under vacuum, l e a v i n g 0.69 g (10θ7ο) of mononitrotoluenes. A gc a n a l y s i s o f t h i s product showed that i t contained 62.12% o - n i t r o t o l u e n e , 0.53% m-nitrotoluene, and 37.35% p - n i t r o toluene; a trace (< 0.1%) of d i n i t r o t o l u e n e was present. 3


2

2

4

P r e p a r a t i o n of DNT

with Nitronium Trifluoromethanesuifonate

Method A. A n i t r a t i n g mixture c o n s i s t i n g of 42.63 g (284 mmol) of C F 3 S O 3 H , 42.75 g of 96% H S 0 , and 7.91 g (126 mmol) of anhydrous HN0 was prepared i n a 100-ml f l a s k equipped with a mechanical s t i r r e r , a d d i t i o n funnel, and thermometer. The s o l u t i o n was cooled to -24°C and 2.02 g (22 mmol) of toluene was added dropwise i n 50 min. As the toluene was added, a s o l i d prod uct was formed and the n i t r a t i n g mixture became p a r t i a l l y f r o z e n . S t i r r i n g was continued f o r 1 hr a t -24° to -20°C and the r e a c t i o n mixture was poured onto 1200 g of crushed i c e . The r e s u l t i n g mixture was e x t r a c t e d with three 250-ml p o r t i o n s of CH C1 ; these were combined and d r i e d (MgS0 ) and the s o l v e n t was evaporated, l e a v i n g 3.83 g (97%) of a l i g h t yellow s o l i d that was i d e n t i f i e d as a mixture o f d i n i t r o t o l u e n e isomers by i t s i r spectrum and elemental a n a l y s i s . Gc a n a l y s i s showed that t h i s product con tained 12.20% 2,6-DNT, 0.45% 2,3- and 2,5-DNT, 86.31% 2,4-DNT, and 1.04% 3,4-DNT. T o t a l meta-isomer content was 1.49%. Anal. C a l c d . f o r C H N 0 : C, 46.16; H, 3.32; N, 15.38. Found: C, 46.12; H, 3.33; N, 15.25. 2

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Method B. A n i t r a t i n g mixture c o n s i s t i n g of 50 g (333 mmol) of C F 3 S O 3 H and 6.3 g (100 mmol) of anhydrous HN0 was prepared i n a 100-ml, three-necked f l a s k equipped with a mechanical s t i r r e r , a d d i t i o n f u n n e l , and thermometer. The mixture c o n s i s t e d of an i n s o l u b l e complex of 2CF S0 H/HN0 i n C F S 0 H . The mixture was cooled to 0°C, and 4 g (43 mmol) of toluene was added over 10 min. The r e a c t i o n mixture was s t i r r e d at 0°C f o r 1 hr and quenched on 500 g of crushed i c e . The r e s u l t i n g mixture was e x t r a c t e d with three 100-ml p o r t i o n s of CH C1 , which were combined and d r i e d (MgS0 ). Removal of s o l v e n t l e f t 7.75 g (98%) of a l i g h t yellow 3

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17.

HILL E T A L .

TNT

Manufacture:

Laboratory

Development

269

s o l i d that was i d e n t i f i e d as a mixture o f d i n i t r o t o l u e n e isomers by i r spectrum. A gc a n a l y s i s o f t h i s product showed that i t contained 17.50% 2,6-DNT, 0.51% 2,3- and 2,5-DNT, 82.84% 2,4-DNT, and 0.95% 3,4-DNT. Method C. A mixture c o n t a i n i n g 6 g (40 mmol) o f t r i f l u o r o methanesulfonic a c i d and 100 ml o f CFC1 was prepared i n a 200-ml f l a s k equipped with a mechanical s t i r r e r , a d d i t i o n funnel, and thermometer. A 1.26 g sample (20 mmol) o f anhydrous HN0 was added a t 25°C, forming the 2CF S0 H/HN0 complex. The temperature of the r e a c t i o n was lowered to 0°C, and 0.46 g (5.0 mmol) o f toluene was added i n one p o r t i o n . The mixture was s t i r r e d f o r 1 hr a t 0°C and poured onto 100 g o f crushed i c e . Three 100-ml CH C1 e x t r a c t i o n s were combined and d r i e d over MgS0 . The s o l vent was removed, l e a v i n g 0.90 g (99%) o f a l i g h t yellow s o l i d that was i d e n t i f i e d as a mixture o f d i n i t r o t o l u e n e isomers by i t s i r spectrum. A gc a n a l y s i s o f t h i s product showed that i t contained 16.47% 2,6-DNT, 0.45% 2,3- and 2,5-DNT, 82.36% 2,4-DNT, and 0.72% 3,4-DNT. T o t a l meta-isomer content was 1.17%. N i t r a t i o n o f D i n i t r o t o l u e n e with 01eum/HN0 Mixtures 3

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The f o l l o w i n g procedure i s r e p r e s e n t a t i v e o f the method used to determine the e f f e c t o f oleum and n i t r i c a c i d c o n c e n t r a t i o n s on the p r e p a r a t i o n o f TNT from DNT. I t i s a l s o r e p r e s e n t a t i v e o f the optimum c o n d i t i o n s used f o r the p r e p a r a t i o n o f TNT from DNT. A mixture o f 11.5 g (182 mmole) o f absolute HN0 and 48.0 g of 30.3% fuming H S 0 (181 mmole o f S 0 ) was heated t o 90°C i n a constant temperature o i l bath. S o l i d 2,4-DNT (11.1 g, 61.0 mmole) was added i n 0.5-g p o r t i o n s over 80 min; t h i s r a t e o f a d d i t i o n maintained a temperature o f 91-92°C i n the r e a c t i o n f l a s k . Stirr i n g and heating o f the yellow s o l u t i o n was continued f o r 1.5 hr a f t e r a l l the DNT had been added. P a r t o f the TNT separated from the s o l u t i o n as an o i l . The mixture was cooled to 25°C with an i c e bath, which caused s o l i d TNT to form, and was then poured i n t o 140 g o f i c e . The product was e x t r a c t e d with methylene c h l o r i d e , and the e x t r a c t was washed with saturated NaCl s o l u t i o n , d r i e d over MgS0 , and evaporated with a rotary evaporator. The s o l i d residue was d r i e d t o constant weight under vacuum over KOH p e l l e t s ; 13.0 g (94.0%) o f TNT was obtained. Gc a n a l y s i s showed the product to be TNT. 3

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N i t r a t i o n o f 2,6-DNT a t 90°C i n a Sealed Reactor T h i s general experimental procedure was used i n the n i t r a t i o n of a l l DNT-isomers to study r e a c t i o n r a t e s and determine the nature


270

INDUSTRIAL AND LABORATORY NITRATIONS

of gaseous by-products at 90°C. A nitrating mixture consisting of 21.60 g of 30.78% oleum (83.1 mmol of S0 ) and 5.19 g of anhydrous n i t r i c acid (82.4 mmol) was prepared at 0° to -5°C in a 100-ml reactor. The temperature was raised to ambient and 2,6-DNT (5.03 g, 27.6 mmol) was added; DNT/HN0 /oleum, 1/3/3. The reactor was connected to the vacuum l i n e , cooled to -196°C, and degassed twice at less than ten microns. The reactor was sealed under vacuum, warmed from - 1 9 6 ° to +45°C. The mixture was then heated from 50° to 90°C in 20 min and held at 90°C for a total heating time of 97 min. The break seal was ruptured and gases were collected in cooled traps during the last hour of nitration. The gases were measured and analyzed by mass spectrometry (CO, 2652 μπιοί; C 0 , 4720 μπιοί). The trap at -78°C contained a trace of brown vapor, which was irreversibly absorbed on Porapak Q, probably N0 . The remaining vapors in this trap were condensed into a hydrazine/ethanol solution and analyzed by uv for TNM; found 1.3 mg. The aqueous acid was extracted with methylene chloride (3 χ 75 ml), combined, washed with brine, dried (MgS0 ), and solvent removed at reduced pressure leaving 5.83 g of a yellow solid. Gc analysis using a 10 ft χ 1/8 i n . 25% Dow 500 column indicated that no residual DNT was present; 100% conversion, 92.9% y i e l d . By consideration of the gases, TNM, and TNT formed, 97% of the DNT was accounted for. 3


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Literature Cited 1.

2. 3. 4. 5.

For good reviews of aromatic nitration, see (a) Hoggett, J.G., Moodie, R. B., Penton, J. R., and Scholfield, K., "Nitration Aromatic Reactivity," Univer sity Press, Cambridge, England, 1971. (b) Olah, G. Α., and Kuhn, S. J., in "Friedel-Crafts and Related Reactions," Vol. III, G. A. Olah, Ed., Interscience, New York, 1964, Chapter XLIII. (c) Olah, G. Α., Accounts Chem. Res. (1971), 4, 240. (d) Ridd, J , H., Accounts Chem. Res. (1971), 4, 248. Hill, M. E . , and Taylor, F., J r . , J. Org. Chem. (1960), 25, 1537. Coon, C. L . , McDonald, G. J., and Hill, M. E . , U. S. Patent 3,788,546 (1973). Coon, C. L . , Blucher, W. G., and Hill, M. E . , J. Org. Chem. (1973), 38 (25), 4243. Coon, C. L . , and Hill, M. E . , U. S. Patent 3,714,272 (1973).


17. HILL ET AL.

Effenberger, F., and Geke, J., Synthesis, 1975, 40. Holahan, F. S., Castorina, T. C., Autera, J. R., and Helf, S., J. Amer. Chem. Soc. (1962), 84, 756.


6. 7.

TNT Manufacture: Laboratory Development


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Industrial and Laboratory Nitrations

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