real world of indwt rial c hemiftry
edited by
W. C. FERNELIUS Kent State University Kent.. OH 44242 ~
HAROLO W~COFF Chem Systems, kc.. 303 South Broadway Tarrytown. NY 10591
The Nitroparaffins Henry 6. H a s 84-51 Beverly Rd., #3G,Kew Gardens, NY 11415 Editors' Note: Although many professors like to think that what is done in their laboratories will be of benefit to others, few of them have the opportunity to see a product of their research became a commercial reality. Following is an account by one who did. Henrv B. Hass. who. with two colleaeues. " , E. B. Hadee and B. M. ~andeibilt,obtained patent on a process to make niiroparaffins in 1934, over half a century ago.
a
The history of the nitroparaffins presents many curious features. The first aliphatic nitro compound was chloropicrin, CCIaN02, made from picric acid, 2,4,6-trinitrophenol, by alkaline hypochlorite oxidation. The great Victor Meyer made nitroalkanes by the reaction which bears his name: RI AgN02 RNDz AgI. After the nitration of aromatic hydrocarhons proved important in establishing the synthetic dye industry, many disappointing attempts were made to nitrate saturated hydrocarhons. Results were meager; mostly oxidation resulted. The use of sulfuric-nitric acid mixtures, effective in aromatic nitrations, proved useless with saturated hydrocarbons. A major problem was presented by the fact that the nitrated product was more soluble in nitric acid than was the starting hydrocarbon and was selectively destroyed. In the 1920's organic chemists in the United States realized that the growing petroleum industry provided a wealth of c h e a ~abundant , raw material. The reaction of chemists varied. The (,pimist said, "1.et's develop a grvat nrw tlrganic chemical industry hasrd on ~erroleurn!"Theoessimistssilid. "The name 'paraffin' means 'little afinity.;These are not very suitable for use as raw materials." The outcome of this argument may be summarized by the fact that about 90% of our total output of organic chemicals is now made from petroleum and its more volatile cousin, natural gas. The writer had been in the natural gas and gasoline business before coming to Purdue University and had discovered in an exploratory test that the free radical NO. reacts with butane a t moderate temperatures. At Purdue I was a assistant professor in a department that had never graduated a PhD. However. President E. C. Elliott had determined that Purdue would hecome a great center for research, and in this he had the backing of the Board of 'l'rustees. I interviewed a young graduate student named Byron Vanderbilt and explained to him that the unique structure of isobutane, with nine primary hydrogen atoms (which were hard to substitute) and only one tertiary hydrogen atom (which was relatively easy to substitute) would be conducive to obtaining good yields of the mononitro derivative. Isobutane had never been nitrated so far as we could discover. So Vanderbilt sealed some nitric acid and isobutane in a Carius tube and heated the mixture to 115OC, a temperature that had often been used for attempted aliphatic nitrations. No reaction! So I said, "Get it hotter; something is bound to happen". At 150 OC a smooth reaction ensued. The expected
+
-
+
tertiary nitrobutane appeared with a melting point a little higher than the literature value due to higher purity. The theory was confirmed, and we were two happy young men. Later Vanderbilt saw a tank of normal butane in the laboratory and, without asking me, tried nitrating butane in the same manner that had been successful for isobutane. He obtained nearly as good a yield of 1- and 2-nitrobutanes as he had previously for (CH3)3CN02with isobutane. This was an unexpected hut happy result. The problem of solubility of the nitrated product in nitric acid had been circumvented by conducting the reaction in the vapor phase. Vanderbilt received his master's degree, took a position in industry, and Edward Hodge continued the research, supported by Phillips Petroleum Company. Hodge suggested trying a flow method that we were using in some chlorination research. Here we had another surprise. When propane was nitrated, we obtained, in addition to l-nitropropane and 2-nitropropane, nitroethane and nitromethane. A plausible mechanism follows. HNO, CH,CH,CH, CH,CH,CH,
CH,CHCH,
+ OH.
OH.
+ NO,
(1)
+ H,O CH,CH,CN,NO, + OH. CH,CH,CH,
+ HNO,
-
+ HNO,
-
CH,CHCH,
-
CH,CH,CH,O.
CH,CH,CH,O-OH CH,CH,CH,O.
CH,CH,.
-
+ HNO,
-
-
I
HCHO
+ OH.
+ OH.
+ CH,CH,.
(2)
(3)
(5)
(8) (9)
formaldehyde
CH,CH,NO,
+ OH.
(10)
The CHsCHy of eq 9 can form hydroperoxide as in eqs 6 and 7. This can split off formaldehyde (as in eq 9) to yield a methyl radical from which nitromethane can form. About a year after we started to get results on the flow method of nitration, Phillips Petroleum discontinued their support. At this point my friend, R.:N. Shreve, suggested to Volume 63 Number 7 July 1986
611
.
Commercial Solvents that thev mieht be interested in this new chemistry. They were making ethanol, butanol, and acetone by the well-known fermentation process invented by Weizmann. (As an aside, this process provided the acetone sorely needed for the English propellant, Cordite, in World War I. T o recognize Weizmann's major contribution to the success of the war effort Eneland promised a homeland to the Jews in Palestine. The raw materials, starch or molasses. were in short s u.. ~ v.l vin Enrland so the process was initiated in the U.S.) A difficulty with the process was that the ratio of acetone to butanol was fixed, and usually one or the other was in surplus. Charles Gabriel of Commercial Solvents came to Purdue to hear about vapor-phase nitration. I did not know until much later why he decided to support our new process. Possiblv it was because acetone can he made from 2-nitropropane to supplement the fermentation source. As i t turned out, 2-nitropropane is more valuable than the acetone that can be made from it, and the fermentation process could not compete with butanol and acetone frompetroleum sources. Commercial Solvents, with the assistance of some of my PhD's who had been trained in nitration chemistry, pushed through the nitroparaffin process to a commercial success. Subsequently, they sold the business to Angus Chemical. A new entrant is W. R. Grace, acompany that announced a $50 million plant for nitroparaffins. By a strange turn of fate they are using NO2 as the nitrating agent, which is what I used in mv -verv.first exneriment. The original nitroparaffin plant of Commercial Solvents at Peoria. Illinois. was replaced bv a laraer - one at Sterlington, Louisana. Here an excess of propane is treated with nitric acid vapors at 370-450 'C and %12 atm in stainless steel reactors. The nitroparaffins are condensed leaving propane and NOz in the gas phase. The propane is then separated and recycled while the NO, is converted t o nitric acid. The mixture of nitroparaffins is washed and fractionated. Reactions The reactions of nitroparaffins had been largely discovered before there was a practical way to make them. As one would expect, nitroparaffins are readily reduced by hydrogen in the presence of Raney nickel to the corresponding primary amines. 3H,
+ RNO,
-
u
RNH,
+ 2H,O
The nitroparaffins are tautomeric substances. RCH,NO=O
* RCH=NO-OH
The acid strength uf the oci form of nitromethane is sumewhat rreater than that of acetic acid. The hiaher nitn~paraffins cave progressively weaker acid strengths than nitromethane. The action of alkaline agents promotes a variety of reactions depending on the reaction conditions Primary nitroparaffins can be hydrolyzed to inorganic nitrites. Condensation to 3,4,5-trialkvlisoxazoles,
Aqueous acids (particularlv sulfuric) convert nitroparaffins tocarhoxylic a c d s and a ~611of hvdroxylammonium ion. Hy altering conditions, it is possible to produce a carhonyl compound together with nitrous oxide. Properties The nitronaraffins are colorless liauids and are soluble in most organic solvents. Some physical properties of the readilv available mononitro comoounds are aiven in the table. - Most organic compounds are soluhie in nitroparaffins. Primary and secondary nitroparaffins react with aldehydes in a sort of Tollens reaction to form nitroalcohols: CH3NOz 3HCHO (HOCHz)&N02. The carbon atoms t o which the nitrogroup is attached in anitroparaffin can be easily chlorinated. Nitroparaffins can be added to double bonds. The nitroparaffins, in contrast to many aromatic nitro compounds, are relatively nontoxic and require no more nrecaution than one would observe in handline " most chemicals. The only mononitroparaffin with significant explosive hazard is nitromethane. The others are too far out of oxygen balance. Although two tank cars of nitromethane have exploded, shipping in drums of suitable metal is safe.
+
uses The nitroparaffins have many uses. Exact consumption is not published but may approximate 100 million pounds annually. As a solvent for cellulose esters, epoxy resins, and many other coating resins, the nitroparaffins have found use in coatines and ~ r i n t i n einks. This is the laraest use for nitropropanes. A: a polar solvent of high d&lectric constant, nitromethane is ~articularlvuseful in the electrostatic spraying of paint: The nitrbparaffins are also important metal cleaning solvents. Nitromethane forms crystalline adducts with salts like A1C13 to yield radical cations. Thus nitromethane becomes an improved medium for FriedelCrafts reactions, although this is largely academic. As a stabilizer for halogenated alkanes, nitromethane prevents corrosion in containers for aerosol formulations. Likewise it is an antigassing agent in aluminum paste formulations for inks and uaiots. A mixture of nkromethane and ammonium nitrate with sensitizer is used as an explosive in mining, oil-well drilling, and seismic exploration. Nitromethane is a superior monorooe ell ant for rocket motors and is used withvarious fuels as H bipropellant. Nitration of the polyalcohol, tris(hydroxymethv1)nitromethane (HOCHdnC-N02, produces a powerful explosive. A recent annouicanentb&cribes theuse of nitromethane in tests as an explosive in underground pipelines. This presumably will provide a means for thwarting advancing tanks in battle. Chloropicrin (now made by the chlorination of nitromethane) and related nitro compounds are useful pesticides. Nlboparaffins Today There has not been much progress in the nitration of paraffins other than those described above. Du Pont, in a
R~RR
and to nitroacetic acid (methazonic acid or nitroacetaldehyde as the intermediate) takes place in basic solution. When nitromethane is treated successively with sodium hydroxide and mercury(I1) chloride, water is lost and mercury(I1) fulminate is formed. The prolonged action of bases on 2-nitrobutane may result in reduction to the oxime, oxidation to the carbonyl compound or dimerization to di-t-vicdinitroparaffin, CzH5(CH3)C(NOz)-C(NOz)(CH3)C2H5. By adding base and then acid, a nitroparaffin is converted in good yields to the corresponding aldehyde or ketone, depending on whether the nitrogroup is attached i n a primarv or a secondarv position. Theaction of Edncentruted mineralacids in theahsenceof water on primary nitroparaffins yields hydmxamic acids. ''
612
Journal of Chemlcal Education
Physical Properties of Nltroparanlns Nitro-
Property
methane
Freezing point, ' C Bdling point. OC Flash point. OF Dielectric const. 30 "C Viscosity, CP at 25 "C Solubility. 25 ' C . % by wt. in water Solubility of water in compound
-26.55 101.20 112 35.87 0.610
Nltr~
elhsne -89.52 114.07 106 28.06
1-Nihopropane -103.99 131.18 120 23.24
2-Nihopropane -91.32 120.25 103 25.52
0.636
0.790
0.721
11.1
4.7
1.5
1.7
2.1
1.0
0.6
0.5
process no longer operative, nitrated cyclohexane either with HN03 in the liquid phase or with NO2 in the vapor phase to obtain nitrocyclohexane, an intermediate in a process for making caprolactam. Some of the major articles of commerce are l-nitropropane, 2-nitropropane, nitromethane, nitroethane, and derivatives such as 2-dimethylamino-2-methyl-1-propranol, 2amino-2-ethyl-1,2-propanediol, and aminotris(hydroxymethy1)methane. 2-Amino-2-ethyl-1,2-propanediol results from the acidcatalyzed condensation of formaldehyde with l-nitropropane followed by reduction of the nitro group. CH&H,CH,NO,
+ 2HCHO CH20H CH,CH,-&-NO,
I
CH20H
n, +
I
CH,CH,--&NH?
1
CH,OH
2-Dimethylamino-2-methyl-1-propanol can he made by reacting 2-nitropropane with formaldehyde.
'7
CH, HCH,
+ HCHO 5
NO, CH,OH cH,-L-cHa
I
, CH&H
(CHhNH
I I N
cHa-cH-cH,
NO* H,C'
'CH,
followed bv reductive alkvlation of the nitro arouv. with dimethylamine. All of the various uses ultimately depend upon an efficient, cheap method of manufacture-of the nitroparaffins. In turn, the availability of the commercial products greatly stimulated fundamental research on the compounds.
Volume 63
Number 7
July 1986
613
