United States Patent (19) 11) 4,189,580 Findeisen (45) Feb. 19, 1980 54 PROCESS FOR THE PREPARATION OF 3,457,293 7/1969 Sonobe et al. ................... 260/465 B NTRILES Primary Examiner-Dolph H. Torrence 75 Inventor: Kurt Findeisen, Odenthal, Fed. Rep. Attorney, Agent, or Firm-Sprung, Felfe, Horn, Lynch of Germany & Kramer 73 Assignee: Bayer Aktiengesellschaft, 57 ABSTRACT Leverkusen, Fed. Rep. of Germany A process for the preparation of a nitrile of the formula (21) Appl. No.: 932,599 22 Filed: Aug. 10, 1978 30 Foreign Application Priority Data wherein R represents an optionally substituted alkyl, Aug. 18, 1977 (DE) Fed. Rep. of Germany as a 2737210 cycloalkyl or aryl radical or an optionally substituted 5 51) Int. Cl. .............................................. CO7C2O/OO or 6-membered heterocyclic radical which may addi 52 U.S. Cl. ................................. 544/301; 260/346.3; tionally be fused with a benzene ring and n' represents 1 260/359; 260/464; 260/465 B; 260/465.2; to 6 which comprises contacting a carboxylic acid of 544/334; 544/356 the formula 58) Field of Search ................. 260/464, 465 B, 465.2, 260/329 R, 346.3,359; 544/301, 334,356 R-(COOH) 56 References Cited wherein R and n' have the meanings given above with U.S. PATENT DOCUMENTS cyanogen chloride and/or cyanogen bromide at a tem 2,800,496 7/1957 Toland, Jr. ....................... 260/465 B perature in the range of 100 to 300° C. 3,012,059 12/1961 Bezman ............................ 260/465 B 3,131,209 4/1964 King ................................. 260/465 B 3,341,566 9/1967 Nakaoka et al. ................. 260/465 B 8 Claims, No Drawings 4,189,580 1. 2 dehydration. However, the high temperatures required PROCESS FOR THE PREPARATION OF of 300' to 500 C. restrict this method to carboxylic NTRLES acids and nitriles which are particularly resistant to heat. (for example J. Amer. Chem. Soc. 38,2128 (1916)). The invention relates to a process for the preparation 5 A further process for the preparation of nitriles was of nitriles by reacting carboxylic acids with cyanogen described in U.S. Pat No. 2,377,795. From low-molecu chloride and/or cyanogen bromide. lar nitriles which are used in a large excess nitriles form A large number of methods are known for the prepa in the presence of an acid, the nitriles corresponding to ration of nitriles. It is possible to obtain nitriles for ex the acids. The disadvantages of this process are the high ample by 10 temperatures and the use of a silver-plated autoclave as the addition of HCN to C-C double bonds, well as the industrially unsatisfactory yields and the use the addition of HCN to C-O double bonds, of low-boiling nitriles, which have to firstofall be synthe the addition of HCN to C-N double bonds, sized. Furthermore, this process seems to be restricted the reaction of alkyl mineral acid esters with metal to the preparation of adipic acid dinitrile. cyanides, the condensation of aromatic diazonium salts 15 A process was found for the preparation of nitriles of with metal cyanides (Sandmeyer reaction), the conden the formula sation of cyanohalogens with Grignard compounds, Friedel-Crafts reactions of aromatic compounds with R-(CN), (I) dicyanogen, the dehydrogenation of amines, the elimi nation of water from aldoximes, the elimination of 20 in which water from amides, the action of ferrocyanide com R represents an optionally substituted alkyl, cycloal pounds or copper cyanide at elevated temperatures on kyl or aryl radical or for an optionally substituted 5- or aromatic halogen compounds, the reaction of ethers 6-membered hetero-cyclic radical, which can addition with HCN or cyanides (Houben-Weyl, Methoden der ally be fused with a benzene ring and organischen Chemie (Methods of Organic Chemistry), 25 n' represents 1 to 6, characterised in that carboxylic 4th edition, Vol. VIII, page 335-338). acids of the formula The preparation of nitriles from carboxylic acids is also described in detail in literature (Houben Weyl, R-(COOH), (II) Methoden der organischen Chemie, 4th edition, Vol. VIII, page 335-338). 30 in which R and n' have the above-mentioned meaning, The preparation of nitriles by the elimination of water are reacted with cyanogen chloride and/or cyanogen from carboxylic acids can be conducted either using bromide at temperatures in the range of 100 to 300° C. chemical means or by thermal methods. Both methods Preferably, in the case of the process according the are associated with a number of disadvantages and have invention, carboxylic acids of the formula (II) are used not been very widely used in preparative chemistry. 35 with n' representing 1 to 3. Alkyl radicals with up to 24 Thus although the ammonium salts of organic acids carbon atoms, preferably with up to 18 carbon atoms, are converted, using water-elimination agents (phos which can optionally be substituted by chlorine, bro phorous pentoxide, glycerol), into nitrile in a heteroge mine, or methoxy, alkoxy-, nitrilo-, methoxycarbonyl nous reaction in order to obtain good yields, it is neces or ethoxycarbonyl-groups may represent the radical R sary to first of all synthesize the amide (Comp. rend. in the above-mentioned formulae. The following op 25,383 (1847) and Ber. 19, 2459 (1886). tionally substituted alkyl radicals may for example be Although nitriles are also obtained by melting acids mentioned: methyl-, ethyl-, propyl-, butyl-, pentyl-, with potassium thiocyanate or lead thiocyanate, the best hexyl-, heptyl-, 2-ethylhexyl-, dodecyl-, tetradecyl-, yields are obtained if instead of the acids their zinc salts hexadecyl-, octadecyl-, -chloro-propyl-, pivaloyl-, ol are used. This method is time-consuming and thus un 45 eyl-, cyanmethyl-, 3-bromopropyl-, co-methoxy-hexyl-, economical because of the lengthy preparation and co-ethoxyhexyl-, co-methoxycarbonyl-butyl- and co drying of these salts (J. Amer. Chem. Soc. 38, 2120 ethoxycarbonyi-butyl-. (1916). Higher molecular fatty acids or dicarboxylic Further, the radical R can represent cycloalkyl radi acids are converted into nitrile when heated with urea cals with up to 10 carbon atoms, preferably with up to or cyanuric acid to temperatures of 250' to 310' C., but 50 6-carbon atoms, which can be substituted by chlorine, the yields are low. They vary between 32% and 49% bromine or methoxy-, ethoxy-, nitrilo-, methoxycarbo (Org. Synth. 25, 95 (1949)). nyl-, ethoxycarbonyl-, methyl-, ethyl-, propyl- or iso A process for the preparation of aromatic nitriles is propyl-groups, or also for arylradicals, with up to 14 known from J. Chem. Soc. 1946, 763, based on the carbon atoms, preferably with up to 10 carbon atoms, reaction of aromatic acids with aryl sulphamides in the 55 optionally substituted by chlorine, bromine, nitro, or presence of phosphorous pentachloride or by heating to methoxy, ethoxy-, nitrilo-, methoxycarbonyl-, ethox temperatures of over 200° C. Both process variations ycarbonyl-, methyl-, ethyl-, propyl-, isopropyl- or tert give very different yields (between 11 and 83%). What butyl-groups. Examples which may be mentioned of is disadvantageous in this process is that per mol of optionally substituted cycloalkyl radicals are: nitrile 1 mol of p-toluene sulphonyl chloride is formed, 60 2-methyl-cyclohexyl-, 4-ethyl-cyclohexyl-2- if phosphorous pentachloride, a substance which is very chlorocyclohexyl- and 4-methoxycarbonyl-cyclohexyl difficult to work with, is used as the condensation agent. , and of optionally substituted aryl radicals: o-, m-, p In the condensation at above 200 C. one mol of p-tol chlorophenyl-, 2,3-dichlorophenyl-, 3,4-dichlorophe uene sulphonic acid and 1 mol of the ammonium salt of nyl-, 4-chloro-3-nitrophenyl-, 2-chloro-4-nitrophenyl-, the p-toluene sulphonic acid are obtained per mol of 65 2-chloro-5-nitrophenyl-, 3,4- and 3,5-dinitrophenyl-, o-, nitrile. m-, or p-tolyl-, 3-methyl-4-nitrophenyl-, 4-tert.-butyl Nitriles can also be prepared directly from organic phenyl-4-methoxycarbonyl-phenyl o-, m-, p-bromophe acids catalytically using ammonia by means of thermal nyl- and 4-ethoxycarbonyl-phenyl-radicals. 4,189,580 3 4. The following may be mentioned as the 5- or 6-mem cyanide, iron-(III)-chloride, tin-(IV)-chloride, alumi bered heterocyclic radicals with up to 9 carbon atoms, num chloride and boron trifluoride. preferably with up to 5 carbon atoms, optionally substi According to the process of the invention nitriles of tuted with methyl-, ethyl-, chloro-, bromo-, nitro-, me the formula (I) can be obtained in good yields and high thoxycarbonyl-, ethoxycarbonyl-, or nitrile, which radi purities. Apart from hydrogen chloride and carbon cal may be additionally fused with a benzene ring: 2,4,6- dioxide no secondary products are formed. Of particu trioxopyrimidyl-, 2,4,6-trichloro-pyrimidyl-, dichloro lar industrial significance is the general applicability of quinoxalinyl-, thiophenyl as well as the phthalic anhy the process of the invention. It is not restricted to partic dride and hexahydrophthalic anhydride radicals. ular carboxylic acids. The working up of the reaction Preferably the following carboxylic acids of the for 10 mixture does not present any problems since the reac mula (II) are used in the process according to the inven tion products are obtained in many cases in such a pure tion: acetic acid, propionic acid, butyric acid, valeric form that a purification process is not required. acid, hexanoic acid, heptanoic acid, 2-ethyl hexanol A further advantage is that the starting products, i.e. carboxylic acid, dodecanic acid, tetradecanic acid, hex the carboxylic acids as well as cyanogen chloride and adecanic acid, octadecanic acid, 3-chloroproponic acid, 15 cyanogen bromide are easily accessible technically. If pivalic acid, 10-undecanic acid, oleic acid, sorbic acid, the products are not available in large quantities they cyanoacetic acid, succinic acid, glutaric acid, adipic can easily be synthesized according to known methods.