AM M0N 0LYSIS ARTHUR C,STEVENSON, E. I. DU PONT DE NEMOURS
COMPANY, WILMINGTON, DEL.
The relatively large number of references appearing during the past year demonstrate an active interest in ammonolysis. Mechanism and kinetic studies dealing with the ammonolysis The relative reaction rate and bimolecu~ar velocity constants for the reaction of methyl acetate and ammonia and primary amines in dioxane solution are listed in Table II. Ratchford and Fisher (66) have studied the ammonolysis of methyl lactate with various primary and secondary amines. Monoalkylamine.; and methyl lactate react readily a t 35" C. Aromatic amines are less reactive and with the exception of dimethylamines, dialkylamines are substantially unreactive. Methyl lactate is much more reactive than methyl acetate and methyl propionate. Branching on the carbon atom next t o the amine nitrogen decreased the yield of amide. The latter effect is illustrated with the selected examples in Table 111. N,N-dialkylacrylamides are prepared (28) by heating methyl acrylate with secondary amines at 250' C. Polymerization is controlled with the use of a small amount of hydroquinone, catechol, or paminophenol. The ester group of acrylic esters example, is unreactive a t temperatures upward t o 100' C.-for &alkoxyacrylic esters undergo replacement of the alkoxy group with secondary amines at less than 100' C. No replacement of the ester alkoxy group is observed. Highly hindered and weak bases are unreactive under these conditions (22).
of esters, the reaction of aniline and methanol, and the ammonolysis of P,4-dinitrochlo~obenzene have contributed much. Studies of process variables for the reaction of aniline with methanol and dimethyl ether have appeared. Aldehydes and ketones have been employed frequently for the preparation of amines through reductive amination. A silica catalyst has effected marked increase in reaction rate for the intermediate Schiff base. Interest continues in the preparation of nitriles via hydrocarbon and ammonia. A n activated carbon catalyst effective at appreciably lower temperature has been developed for this reaction. The useof water vapor in anadiabatically controlled system effects marked improvement in conversion to nitriles. Hydrogen, ammonia,and carbon monoxide have been converted to amines through application of the O x o process.
I N the past, this review has not been limited to ammonolysis in the narrow sense. The reaction of ammonia with olefins and alkyl hydrocarbons t o form nitriles, and reactions involving both aliphatic and aromatic amines have been included in order t o give a more nearly complete treatment of the application of this unit process.
AMMONOLYSIS OF ESTERS Baltzly et al. (6) have studied the ammonolysis of esters with primary and secondary amines. Ammonolysis of methyl, ethyl, and isopropyl acetates was effected with primary and secondary n-butylamines in alcohol, dioxane, and methyl acetate solvent systems. Methanol was found t o be the preferred solvent. The bimolecular reaction rate constants for a number of butylamines in methanol are compared at 10% completion in Table I. The reaction rate constants were observed t o diminish as the reaction proceeded.
PREPARATION OF AMINES ALCOHOLS
I n investigating activated bauxite as a vapor phase dehydration catalyst, Heinemann et al. (40)have studied the conversion of butyl alcohol t o butylamines. Conversion ranged upwards to 58,8y0 depending on the conditioiis used. With a 58.870 conversion, the product consisted of 35.25% primary amine, 49.25% secondary amine, and 15.5% tertiary amine. Liquid space velocities of 0.3 to 0.4 per hour were used with ammonia-alcohol ratios ranging between 1.5 to 1 and 3 t o 1 and a temperature of 320' C. The greater ammonia to alcohol ratios favor primary amine formation. Lower temperatures and higher space velociPrimary amines under these conditions are more reactive than ties result in lower conversions. Olefin production becomes ammonia, while secondary amines are less reactive than either the primary reaction at temperatures in excess of 320' C. The primary amines or ammonia. The lower reactivity of the secondtemperature of activation and the iron oxide content of the ary amines is the result of stearic factors. catalyst are important for optimum activity. An activation Arnett et al. ( 1 ) have investigated the ammonolysis of esters temperature of 425' C. and ferric oxide content of 3y0 are prcwith primary amines in anhydrous dioxane solution in which ferred. the reaction rate is inherently slow. Three factors were found Olin (66)has converted 2-hydroxypentamethylene oxide to 5to be of importance in determining the reaction rate: (1) basicity aminopentanol or the N-alkyl derivative in yields ranging from of amine; (2) steric effects influencing the attachment of the 79 to 92% of theoretical, based on 2-hydroxypentamethylene amine t o the carbonyl carbon atom; and (3) the presence of a oxide. The reaction is carried out by treating '2-hydroxypentacatalyst-e.g., ethylene glycol. A scheme for the reaction methylene oxide with ammonia or alkylamines in methanol mechanism is suggested as follows: solvent under hydrogen pressure and in the presence of a hydrogenation catalyst. U Diethylene glycol and ammonia react II + Ra t 205' c. in the presence of a hydrogena+ -----) R"-C-N-R + R"@H H-N: + RW- -OR"' R' tion catalyst-e.g., nickel on kieselguhrA t to form @-( @-hydroxyethoxy)ethylaniine. Good yields are reported (65).
Table
1.
Bimolecular Reaction Rates for Ammonolysis of Methyl Acetate in Methanol [lo% completion (6)l Amine k 10% X 10s n-Butylamine 15.1 Iaobutylamine 6.3 Methyl n-butylamine 0.11 Methyl isobutylamine 0.018
co
E
k
1920
September 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
Table [I. Bimolecular Velocity Constants and Relative Reaction Rates for Ammonolysis of M e t h y l Acetate in Dioxane Solution ( 7 ) Av. Velocity Amine Constant, k Relative k, '?& Methyl 8.53 X lo-' 100.00 Ethylenedi2.38 x 10-9 27.9 Monoethanol1.16 X 10-2 13.6 Ethyl13.0 1.11 x 1 0 - 9 n-Butyl12.4 1.06 X 10-9 n-Amyl11.6 9.87 x 10-3 n-Propyl8.79 x 10-3 10.3 Isobutyl4.35 x 10-3 5.10 8-Phenylethyl3.75 3.20 x 10-3 Allvl2.06 x lo-: 2.42 BGiyl1.65 X 101.93 Ammonia 1.33 x 10-3 1.56 Isopropyl 4.22 x 10-4 0.495 sec-butyl 0.267 2.27 x 10-4 tert-butyl
Table
111.
Immeasurably slow
N-Substituted Lactamides from Primary and Secondary Amines (62) % Yield Based on Amine n-OctylIsobutylBenzylCyclohexylIsopropyl-
Unrecovered Ester
96.0 95.6 94.0 92.0 83.0
Epichlorohydrin is converted in two steps t o 3-dialkylaniinc-2hydroxypropylamine in a n over-all yield of 34.67,. The starting material reacts first with a dialkylamine in a n inert solvent t o give I-dialkylamino-2,3-epoxypropane. This intermediate compound reacts with aqueous ammonia at 100" C. to yield the product (36). Fowler (SO) has shown improvement in yields of 1,Zdiaminopropane from ammonia and I-amino-2-propanol by carrying out the reaction in the presence of hydrogen and a hydrogenation catalyst. I n carrying out the reaction under 1100 pounds per square inch of hydrogen pressure at 180' C. with 25% excess ammonia, a 65y0 yield of 1,Zdiaminopropane was obtained, Gresham and Shaver have investigated the reaction of aliphatic 8-lactones with ammonia, and primary and secondary amines to form the corresponding 8-aminocarboxylic acids (31-34). The reaction is carried out in solvents-e.g., alcohols, ethers, and acetonitrile-at essentially room temperature. Thus, 8-propiolactone in acetonitrile reacts with cyclohexylamine at room temperature to give a 95% yield of substantially pure 8-cyclohexylaminopropionic acid (3.2). Likewise, mono- and diethanolamines react with 8-propiolactone t o give the corresponding mono- and diethanolaminopropionic acids in yields ranging from 51 to 65% of theoretical (34). Similarly, reaction with ammonia is effected in butyl alcohol at 16' C. with a 797" yield of 8-aminopropionic acid (31). ALDEHYDES AND KETONES
Interest has continued in the use of aldehydes and ketones as intermediates for the preparation of amines. Dombrow (26) shows improvement in yield of the intermediate Schiff base with the use of an acid-treated silicate catalyst-for example, aniline and methylisobutyl ketone react in liquid phase at the reflux t o the extent of 83% of theoretical in 3 hours in the presence of catalyst, whereas in the absence of catalyst, the reaction is only 24% complete in 11 hours. Daasch and Hanninen (18) have shown by means of infrared spectra that the condensation of aromatic aldehydes and ethanolamine leads to the corresponding Schiff base instead of an oxazolidine structure. With the use of hydrogenation conditions in the condensation of amines and aldehydes, the intermediate Schiff base is converted t o the corresponding amine. Both anhydrous and
1921
aqueous systems are used in effecting the reaction. Ammonia or the amine is used in excess and Raney nickel is frequently used as the hydrogenation catalyst. Acrolein, which is previously hydrated by treatment with water a t 110' C., reacts with anhydrous ammonia and hydrogen under approximately 1500 pounds pel square inch at 100" C. in the presence of Raney nickel catalyst with a 26.5% conversion to 1,3-diaminopropane (4). The ultimate yield bascd on the starting acrolein is 51%. Dibenzyl ketone in methanol solution is converted t o dibenzylmethylamine by treatment with anhydrous ammonia and hydrogen in the presence of a hydrogenation catalyst (69). With the use of a n aqueous system, 3-methyl-3-butanol2-one is converted t o Zamino-3-methyl-3-butanol in essentially theoreticd yields (69). T h e reaction is effected a t 70" 6 . with 4.6 moles of 28% aqueous ammonia, under hydrogen pressures which range from 500 to 1350 pounds per square inch. Raney nickel is used as the hydrogenation catalyst. Loder and Gresham ( 4 8 )have reacted di(alkoxymethoxyalky1)amines with ketones and aldehydes under hydrogenation conditions ranging up t o 200' C. and 1000 atmospheres of pressure to obtain the corresponding tertiary amines-for example, di(isobutoxymethoxyethoxyethy1)amine reacts with formaldehyde in methanol solution at 102' C. end 400 atmospheres of hydrogen pressure with a 96% conversion to N-methyl-di(isobutoxymethoxyethoxyethy1)amine. Similarly, di(ethoxymethoxyethg1)amine reacts with acetaldehyde and acetone with somewhat lower yields (49). Brimer et al. (10) have prepared n-butylamine in yields of 91% of theoretical by reacting n-butyraldehyde and ammonia in the presence of hydrogen and a hydrogenation catalyst. The reaction is carried out at 135' to 165' C. at 500 pounds per square inch of hydrogen pressure. The reductive amination of cyclopentylacetone with methylamine is effected a t 2000 pounds per square inch at 135" to 150' C. in the presence of hydrogen and Raney nickel ( 6 4 ) . Clark (19) has devised a process for the synthesis of aliphatic amines which contain 1 to 12 carbon atoms, through a modified oxo process. The feed gases comprise 2 to 10 mole 7 0 ammonia, hydrogen, and carbon monoxide. The amount of hydrogen varies between 1 and 2 moles per mole of carbon monoxide. Catalysts employed include cobalt, iron, and nickel. Thoria and kieselguhr are effective promotcrs for cobalt and nickel catalysts; potassium oxide is effective for iron. With the cobalt catalyst, thk reaction takes place at 182" t o 221' C. il pressure of 150 pounds per square inch and a space velocity of 70 to 140 per hour are employed. The composition of the synthesis gas is as follows: 15.6 mole yo ammonia, 52.4 mole % hydrogen, 25.6 mole yo carbon monoxide, and 2.5 mole % nitrogen. Hydroabietylamine is prepared from hydroabietylaldehyde by treatment with anhydrous ammonia in the presence of hydrogen and a hydrogenation catalyst. Conversion of the aldehyde t o the amine is judged to be 67% complete (7). I n examining the Wallach reaction, which involves formic acid reduction of a Schiff base, as a route t o secondary amines, Baltzly and Kauder ( 6 ) conclude that i t is occasionally serviceable but not superior t o other alternative procedures. It has been used successfully in the preparation of dimethyldodecylamine in 91% yield (based on dodecylamine) by treating dodecylamine with a mixture of formic acid and formaldehyde in a water-alcohol system (15).
PREPARATION OF ARYLAMINES Evans and Bours (29) have investigated the formation of dimethylaniline b y the vapor phase reaction of aniline and methanol, and aniline and dimethyl ether. Activated alumina was the most efficient catalyst. The route involving dimethyl ether is preferred because of higher yields and a purer product.
1922
INDUSTRIAL AND ENGINEERING CHEMISTRY
Aniline and dimethyl ether in the ratio of 1 t o 5 moles react over a n Alco activated alumina catalyst at 275' t o 285' C. to give a quantitative yield (based on aniline) of dimethylaniline of 99% purity. A pilot plant with a capacity of 4 to 5 pounds per hour was constructed and operated. The preparation of dimethylaniline from aniline and methanol with sulfuric acid as catalyst has been investigated by Shreve et al. (66) with the objective of determining the effect of several variables--i.e., time, catalyst concentration, temperature, ratio of reactants, free board. The variation of the reaction rate constant with the catalyst concentration is represented accurately by the equation k = koz (1-O.52), where z is the fraction of the amine present in the form of a sulfuric acid salt. Temperatures in excess of 230" C. were found to cause side reactions. The variation in reaction rate with temperature is expressed in the following equation: -12 106 ko = 6.0 X 101' e
Vol. 43, No. 9
form the corresponding aminonitroalkanes ( 2 , 3). In this manner, 3-nitro-3-hexene and 1-nitro-1-butene react with ammonia t o form the corresponding 3-amino-4nitrohexane and 2-amino-l-nitrobutane, respectively.
REACTION OF AMINES WITH AROMATJC CHLORO COMPOUNDS Hughes et al. (41) have studied the effects of a number of variables in the process for the continuous manufacture of Nmethylaniline from chlorobenzene and methylamine, first reported in the third annual Unit Processes Review. One of the novel features of this procedure provides for recycling the copper catalyst without isolation. Copper is the most effective catalyst. Little difference was observed between cuprous and cupric copper. The minimum temperature for the reaction is 215" C. and the preferred molar ratio of methylamine to chlorobenzene is 5 t o 1. Conversion of chlorobenzene is approximately 90% per pass. The reaction of a number of alkylamines and dialkylamines with chlorodinitrobenxene in alcohol solution has been studied by Brady and Cropper (9). Remarkable differences in rate constants have been observed. These differences are not directly related to the base strengths. The rate constant for the reaction with dimethylamine is more than 30,000 times that for diisopropylamine which is a stronger base. These data indicate t h a t steric factors play an important part in determining the rate constants. A reaction mechanism involving nucleophilic attack of the saturated carbon atom carrying the chlorine is suggested. Reaction rate constants for the reaction of 2 , P dinitrochlorobenxene with several amines in 99% alcohol at 25' C. are given.
--. il'
The rate constant is only slightly decreased by decreasing the mole ratio of methanol to aniline from 3 t o 1 t o 1.5 t o 1. Increasing the mole ratio of methanol to aniline increases slightly the equilibrium conversion. Using 50% excess methanol, the equilibrium conversion is 99% at 200" C. Heinemann et al. ($9,40) react aniline and ethyl alcohol in the vapor phase in contact with a bauxite catalyst at 530' F. A catalyst containing approximately 6yo ferric oxide, which is activated a t 1000' to 1200' F., is preferred. Optimum conditions result in a n 87.2% conversion of aniline. The product is composed of 96.3y0 ethylaniline and 3.7y0 diethylaniline. Diarylamines are produced by heating primary aromatic amines in the liquid phase in the presence of ferric or aluminum halide catalysts-for example, a 59.6% yield of diphenylamine is obtained by reacting aniline at 304' t o 357' C. at 160 pounds per square inch in the presence of aluminum chloride (27). Aniline and hydroquinone react a t 300" C. in the presence of trialkyl phosphates or trialkoxyethyl phosnhate which function as catalvst~i(1L. 7f). A 75.6% yield, based on hydroquinone, of h',N'-diphenyI-p phenylenediamine is obtained (7f). Para-substituted anilines react with formaldehyde and hydrogen in the presence of a platinum catalyst to form a substituted dimethylaniline-for example, p-dimethylaminoacetophenone and p-dimethylaminobenzoic acid are obtained in 70% and 87y0 yields, respectively (57).
0
J
-
o :C1
I
I
N On
NOz
on;?;--(-) :Gn2~ +
REACTION OF AMINES WITH OLEFINIC COMPOUNDS Potassium and sodium metals are effective agents for the reaction of mono- and dialkylamines with vinyl esters. The metal reacts first with the amine to form an intermediate alkali metal amine which then reacts with the unsaturated ester to give the corresponding p-dialkylaminoethyl ester (20). This procedure is likewise applicable to conjugated alkadienes-for example, after treating 0.5 mole of sodium metal with 2 moles of n-butylamine a t 10-1' C., subsequent reaction with butadiene was carried out at 50" to 75' C. over several hours. The products of the reaction were n-butylbutenyloctatlienylamine and N-butyldibutenylamine (29). Langkammerer (46) has prepared p-B-tert-aminoadiponitriles by reacting 1,sdicyanobutene with secondary amines. The reaction is effected at approximately room temperature. Yields range from 60 t o 80%. Similarly, olefin sulfides have been converted t o secondary and tertiary aminothiols by treatment with primary and secondary amines--e.g., n-heptylamine and isoh t y l e n e sulfide react at reflux temperature to give a 49.3% yield (based on isobutylene sulfide) of n-heptylamino-terthutylthiol ( 7 2 ) . With di-n-heptylamine, the corresponding yield is 62.25% of theoretical (72). Xitroalkenes react with anhydrous ammonia or primary and scrondary amines in alcohol or ether solutions at 25' t o 35" C. t o
+ + :NR,H +OzN c>,:':cl ':NR,H NRzH O,N
O-NR, + H:~-R,H
ko, Ammonia and primary amines replace the %nitro group in 6halo-2,3-dinitro-pcymene, whereas, secondary amines replace the halogen. Thig difference in the course of the reaction is presumably due to steric factors (56).
PREPARATION OF NITRILES HYDROCARBONS
The preparation of nitriles by the vapor phase reaction of ammonia, and olefins, and alkyl aromatic hydrocarbons continues to capture the interest of investigators. Experimental data concerned with the conversion of toluene to benzonitrile have been summarized by Denton et al. (83)of Socony Vacuum Oil Co., the forerunners in this field. The reaction is effected over a catalyst composed of molybdic oxide supported on alumina. The temperature of the reaction is critical in the range of 975" to 1025' F. Space velocities and molar ratios of the reactants are not critical and may be varied over a wide range. Optimum pressures range from less than atmospheric to atmospheric. Conversions per pass vary from 5 to 10% based on the weight of toluene charged. Ultimate yields range between 60 and 85 weight yo,based on the toluene consumed. New developments in the reaction of alkyl aromatic hydrocarbons and ammonia t o form the corresponding nitriles deal with development of new catalysts, the use of air and water vapor in the reaction mixture, and the effect of carrying out the reaction adiabatically instead of isothermally. Activated carbon functions as a catalyst at 600" t o 800" F. when 15% of air by weight based on the toluene is used in the reaction mixture (44). Silica supported on alumina bead catalyst has been developed
September 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
\vhic.li is c~fft~c.tivc itt !)OOo to 1075" (:. in systrnis involving l5CL of air based on the weight of tolucnc! in the mixture (45). Klimitas and Itasmusseii ( 4 2 ) have found marked impi'ovements in yield in the convctrsion of toluene and ammonia by carrying out the reaction acliabatically instead of isothermallv over a molybdenum oxide-alumina catalyst, in thc presencc of IL small amount of ivater vapor. This circct is c~learlyillustrated in Table IV where the ultimatt, j k l d is increased from 51 to 70%. The beneficial effect of the 0-ater vapor is not observed if the reaction is carried out isothermally.
Table IV. Adiabatic Conversion of Toluene and Ammonia O v e r Molybdenum Oxide-Alumina Catalyst Water Vapor, ' P c I I I ~ . ,c/o Raved on 12. Toluene 0 0 $171 Oxo 1 0
C'iitalynt
NI18:Tolriene
Ratio 1 03 1 04
Liquid Space Velocity/ Hour 2 48 2 48
Yield/ Pass 3 11 4.87
Ultimate Wt. Yield,
70
,5 1 0 70 0
I>cwtoii and Plank find that promotion of a molybdenum osidr-alumina catalyst with the oxides of a large number of metals-e.g., copper, beryllium, or silica to the extent of 0.5 to 5'3, based on the weight of molybdenum oxide-is effective in incareasing the conversion per pass as much as 4575 of that obtained when using unpromoted catalyst (24). \Vith the use of olefins as starting materials for the preparation of nitriles, reduced metal oxide catalysts supported on an inert carririr are emplo>wi (73)-for example, a 27.8$Z0 yield of nitides (calculated as propionitrile anti based on the propylene fed) is obtainrd Lvhen carrying out thc reaction in contact with cobalt 01' nic.kcl c:italyst a t 6.10' F.anti 1500 pounds per squaw inch \\.it11 a spa(*evelocity of 0.2 1 ) hour. ~ T h c osidc of one or more of thr following metals, aluminum, intlium, thallium, titanium, ziuwnium, or thorium suppoi~tetion silic,:t is effcctivc in converting olc.fins to riitrilos. In this nimner, 3 r n o l ~ 3of amnionia and 1 of proliylc~ncreart a t 1165' to 1200" F. at a i~)rosiina t el y at mosphrLric, p i urr over a catalyst c-onsisting iliva, 1Oyozirconia, 4Yo alumina, and 2mo moistuw. A 9 \.icld of acetonitrile por pass (bascd 011 prop~'lc~1ic~) is oi)t:iiiiui (;73). O T H E R ROUTES TO NITRILES
Swondary and tertiary aldeh~-desreact xith ammonia. in this ~.i~1)oi' phase at 500c to 850" C. over a copper promoted alumiii:t 01' silica c,atalyst. Isobutyraldch\de and 5 parts of ammonia rvart at 670" to 780" F. over a c-oppcr-alumina catalyst to give a 25 iiiolc To conversion to the corresponding nitrile. The mntact convcrtime is 1.5 seconds. IVith lienzaldchyde, a 46 mole sioii to bcnzonitrile is obtained ( 6 1 ) . Ralston et al. (61 ) prepared nitriles by roacting carboxylic' acids and ammonia in the presence of red phosphorus catalyst. o-Dinitrilcs have bccm pi~c~parcd from the corresponding anh>drides. The rcaction is carried out in the liquid phase in a tertiary base--c.g., p\.ridinc. An intermediate amnioniuni salt of the nionoarnide is dehydrated in pyridine solution 11). treatmont with phosphorus o hloride. Both steps in the reaction arr oH'rcted at less than 100" C. at atmospheric p ~ ~ e s s u r t ~ . The i.eartion is particularly adapted to compounds having high molecular \veights which are not suited for vapor phase rea
