Abstract:
Nitriles are produced from carboxylic acids and ammonia utilizing an intermediate nitrogenous base-carboxylic acid complex by reacting said complex with ammonia at a temperature of from about 200° to about 800°C. The nitrogenous base is de-complexed as the nitriles are produced, recovered and recycled.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 386,788 filed Aug. 8, 1973 and now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the general field of the production of nitriles, and specifically to the production of nitriles from corresponding carboxylic acids. 
     2. Description of the Prior Art 
     The preparation of nitriles from carboxylic acids and ammonia is well known. Catalysts which have been used include bauxite (Heinemann, et al., Industrial Engineering Chemistry, 41, 2928-31 (1949)); aluminum oxide at 200°-400°C (USSR Pat. No. 260,628); phosphates (Swiss Pat. No. 351,263); phosphates (German Pat. No. 1,046,015); and silica gel at 400°-500°C (Organic Synthesis, Vol. IV, page 62). 
     The above reactions are quite useful in preparing high yields of nitriles from the corresponding carboxylic acids. However, some acids, such as phthalic, isophthalic, terephthalic, benzoic, and toluic, are difficult to handle because their melting points are quite high, ca. 122°-425°, and they tend to sublime readily from the melt. The actual physical handling of such melts, e.g., metering, pumping, transferring, etc. presents a host of problems requiring special equipment, sophisticated techniques, and constant attention. 
     Many of these problems could be alleviated if a suitable reaction mixture were used. This invention demonstrates that complexes formed between heterocyclic nitrogen compounds, such as pyridine, quinoline, etc., and tri-substituted amines, such as triethylamine, and carboxylic acids, are useful in overcoming these problems. 
     The present invention solves the problem of charging the high-melting carboxylic acids, providing thereby a process for converting both low and high-melting carboxylic acids to the corresponding nitriles, by using a carboxylic acid-nitrogenous base complex. Substantially all of the nitrogenous base can be recovered from the reaction mixture because they do not recomplex with the nitriles produced. In addition, the nitrogenous bases are selected such that they do not react with ammonia at the reaction condition. 
     SUMMARY OF THE INVENTION 
     Nitriles are prepared from the corresponding carboxylic acids nitrogen base-carboxylic acid complex. Preferably, the complex is reacted with ammonia at a temperature of from about 200° to 800°C. The reaction preferably takes place in the presence of silica gel or alumina. A particularly advantageous feature of nitrogenous invention is the recovery of substantially all of the nitrogeneous base, as it does not take part in the nitrile reaction. 
     UTILITY OF THE INVENTION 
     Nitriles have great commercial importance as solvents and as chemical intermediates. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The nitrogenous bases used to form the complexes with carboxylic acids used in the process of this invention have no replaceable hydrogen atoms and are unreactive with the carboxylic acids in the sense of forming amides or nitriles. However, the compounds do react with the acids by forming an acid-base complex as described below. It is preferred that the nitrogenous bases described in this invention be at least about as basic as pyridine and that they be a liquid at ambient temperature (e.g. 20°C). The nitrogenous bases of this invention are tri-substituted at the nitrogen atom and comprise heterocyclic nitrogen compounds such as pyridine and tri-substituted amines. 
     By &#34;complex&#34; is meant a compound which is made up structurally of two or more compounds or ions, that is, a compound formed by a combination of substances that are themselves capable of independent existence. More specifically, in the present invention, &#34;complex&#34; is used to describe the chemical moiety produced by the interaction of carboxylic acid with nitrogenous base. The chemical literature often describes such complexes as hydrogen-bonded complexes. In most cases, the complexes of the invention are liquids and are thus easily handled. Previous workers have used solids, e.g., the ammonium salt of the acid which has proven to be intractably difficult to handle mechanically because it is a high melting solid. Though the Applicant does not wish to be bound by any particular mechanism hypothesized herein, it seems probable that the liquid complex of the present invention enters the reaction zone and is thereupon virtually immediately disassociated by contact with ammonia as well as by the influence of the temperature of the reaction zone. The reaction with the ammonia then proceeds practically exactly as though the more difficultly handled ammonium salt of the acid had been introduced. 
     The complexing of the carboxylic acids with the nitrogenous base is believed to be due to the acid-base type reaction as shown in Equation 1, v,10/20 
     where δ indicates partial charge, the δ + and δ - denote partially developed charges rather than fully developed or formal charges, e.g., see Jack Hene, Physical Organic Chemistry, 2nd Ed., McGraw-Hill Book Co., Inc., (1962) p. 286. 
     It is theorized that similar complexes are formed between tri-substituted amines and carboxylic acids. It is further theorized that the complex (Equation 1) is broken down when contacted with ammonia at the elevated reaction temperatures. The carboxylic acid is thereby freed for reaction with the ammonia. 
     It is preferred that the boiling point of the nitrogenous base be low compared to that of the resulting nitrile so that it can be readily separated and recovered by distillation of the reactor effluent. Pyridine is the preferred complexing agent because it has a relatively low boiling point and forms a liquid complex with large amounts of acid, for example, toluic acid forms a liquid complex at room temperature with pyridine containing up to 40 percent of the carboxylic acid. 
     Thus, this invention teaches production of nitriles from carboxylic acids using a carboxylic acid-nitrogenous base complex as the raw material. The basic nitrogenous compound in the complex is preferably pyridine or an alkyl derivative of pyridine. The nitrogenous base may also be quinoline or alkyl derivative of quinoline. In addition, the nitrogenous base may be a tri-substituted amine. Mixtures of the above mentioned compounds are also suitable for forming complexes. More preferably, the alkyl derivatives of pyridine and quinoline are lower alkyl derivatives containing from 1 to about 6 carbon atoms in the alkyl group(s). Preferably, the tri-substituted amine contains from 1 to about 8 carbon atoms per alkyl substituent. Upon forming the carboxylic acid-nitrogenous base complex, the raw material is preferably contacted with ammonia at a temperature of about 200° to about 800°C., and more preferably from 400° to 600°C. The ammonia may be contacted with the raw material in the presence of an alumina or a silica gel catalyst. 
     The invention may be practiced in the vapor or liquid phase by maintaining the reaction zone at appropriate pressures to maintain the reactants in the desired phase. The vapor phase will be preferred. The invention can be practiced in the presence of dehydration catalysts, e.g., silica gel, alumina, etc., but such catalysts are not necessary. 
     The carboxylic acids useful in forming the complex in this invention include, but are not limited to, high-melting carboxylic acids, polycarboxylic acids, and substituted carboxylic acids, preferably alkyl substituted carboxylic acids. 
     Among the preferred aromatic carboxylic acids are phthalic, isophthalic, terephthalic, benzoic and o, p and m-toluic. Other preferred carboxylic acids are linear C 4  -C 14  dicarboxylic acids, such as malonic, succinic, adipic, suberic, pimelic, azelaic, sebasic, undecanedioic, dodecanedioic, tridecanedioic, tetradecanedioic, maleic, fumaric, and citric acids. The mole ratio of the ammonia to the carboxylic acid in the complex is about 3 to about 15 moles of ammonia per mole of carboxylic acid. After contacting the complex with ammonia, the nitriles thus produced are recovered and preferably the nitrogenous base is recycled. 
     The conditions for forming the complexes themselves are not narrowly critical and will vary according to the particular carboxylic acid and nitrogenous base selected. However, in general, from about 100 to about 1, more preferably from about 10 to about 1, and most preferably from about 1 to about 1 moles of nitrogenous base will be reacted per mole of carboxylic acid and a complex will be formed at a temperature of about -50° to about 200°C, more preferably from about 0° to about 100° and most preferably from about 25° to about 75°C and at a pressure of from about 0.1 to about 100, more preferably from about 0.5 to about 50 and most preferably from about 1 to about 10 atmospheres. 
     It should be understood that the invention is capable of a variety of modifications and variations which will be made apparent to those skilled in the art. 
     EXAMPLES 
     EXAMPLES I-V 
     A stainless steel, tubular reactor, 36 inches long and 1.0 inches in diameter, is filled with 4-8 mesh silica gel and heated to 480°C. A complex containing equal quantities (by weight) of carboxylic acid and tri-substituted nitrogenous base is then charged to the reactor at a rate of 85.4 ml/hr. Ammonia if fed to the reactor at a rate of 2400 cc/hr. After 4.1 hours, 350 ml of the complex is charged to the reactor. Under these conditions, the following results were noted: 
     
         FEED                         OUTPUTExample            Tri-SubstitutedNo.  Carboxylic Acid          Wt. %              Nitrogenous Base                        Nitrile   Recovery                                          Base Recovery__________________________________________________________________________1    p-toulic acid          50% pyridine  p-tolunitrile                                   91.8%                                       almost quantitatively2    p-tert butyl-          30% pyridine  p-tert-butyl-                                  &gt;90.0%                                       essentially quantitativelybenzoic acid            benzonitrile3    terephthalic          25% pyridine  terephthalonitrile                                  Good Goodacid4    p-toluic acid          40% 1,4 dimethyl                        p-tolunitrile                                  Good Good              quinoline5    terephthalic          30% triethylamine                        terephthalonitrile                                  Good Goodacid__________________________________________________________________________