United States Patent (11) 3,624,157 72 inventors Raymond W. Ingwatson; 2,965,682 12/1960 Horvath ....................... 260/651 R Nathan Dale Ledford, both of Chattanooga. 3,087,967 4/1963 Graham et al................ 260/599 Tenn. 3,238,243 3/1966 Falbe et al.... ... 260/651 RX 2 Appl. No. 886,022 3,467,697 9/1969 Kohll et al.... ... 260/651 RX 22) Filed Dec. 17, 1969 3,524,885 8/1970 Deinet.......................... 260/599 45) Patented Nov.30, 1971 FOREIGN PATENTS 73 Assignee Welskol Chemical Corporation Chattanooga, Tenn. 9. 107 21908 Great Britain................ 260/599 Primary Examiner-Bernard Helfin Attorney-Robert J. Schwarz 54 PROCESS FOR PREPARNG ORTHO CHOROBENZALDEHYDE ABSTRACT: This invention discloses a process for preparing 9 Claims, No Drawings orthochlorobenzaldehyde which comprises chlorinating the (52 U.S. Cl........................................................ 260/599, side chains of a mixture of ortho- and para-chlorotoluene con 260/651 R, 260/515A taining from about 50 to about 85 percent by weight of the 51 ) int. Cli........................................................ C07c47,154 orthoisomer in the liquid phase with chlorine gas until the 50 Field of Search............................................ 260/599, ratio of orthochlorobenzal chloride to parachlorobenzal 651 R, 515 A chloride in the reaction mixture is at least about 10 to 1 by weight, hydrolyzing the resulting mixture to the corresponding 56) References Cited benzaldehyde and benzoic acids and thereafter recovering the UNITED STATES PATENTS orthochlorobenzaldehyde therefrom. 2,816, 44 l2/1957 Harris........................... 260/651 RX 3,624,157 1. 2 PROCESS FOR PRE PARING ORTHO orthochlorobenzaldehyde product of at least 90 percent purity CHLOROBENZALDEHYDE and as high as about 99 percent purity depending upon the This invention relates to a chemical process and more par isomer ratio of the starting materials and the particular degree ticularly relates to a method of preparing orthochlorobenzal to which the chlorination was carried out can be obtained. dehyde from a starting mixture of ortho- and para 5 Thus, one embodiment of the present invention resides in a chlorotoluene. process for preparing orthochlorobenzaledehyde which com Chlorobenzaldehyde is readily prepared by the hydrolysis of prises chlorinating the side chains of a mixture of ortho- and chlorobenzal chloride. Chlorobenzal chloride is prepared by para-chlorotoluene containing from about 50 to about 85 per the side-chain chlorination of the corresponding cent by weight of the orthoisomer in the liquid phase with chlorotoluene. The chlorotoluene in turn is prepared by the O chlorine gas until the ratio of orthochlorobenzal chloride to ring chlorination of toluene. This ring chlorination of toluene parachlorobenzal chloride in the reaction mixture is at least however results in the formation of an isomeric mixture and about 10 to 1 by weight, hydrolyzing the resulting mixture to predominantly in a mixture of ortho- and para-chlorotoluene. the corresponding benzaldehyde and benzoic acids, and Thus, in order to prepare orthochlorobenzaldehyde free of its thereafter recovering the orthochlorobenzaldehyde paraisomer by the above-described route it is necessary to 15 therefrom. start with pure orthochlorotoluene or perform a separation on the isomeric product mixture. The ratio of ortho- to para-chlorobenzal chloride in the Orthochlorotoluene free from its paraisomer is difficult to reaction mixture can be readily determined by standard prepare since the isomeric mixture obtained from the ring analytical procedures. The method which is particularly suita chlorination of toluene is not readily separated into its in 20 ble for this purpose is a gas chromatographic analysis whereby dividual components. The similarity in boiling points of ortho relative proportions of components are simply ascertainable. and para-chlorotoluene requires distillation equipment having As indicated above, the chlorotoluenes are side chain about 100 theoretical plates for complete separation. The chlorinated to an extent that the ratio of ortho- to para present invention obviates the use of such highly expensive chlorobenzal chloride contained in the product mixture is at equipment. 25 least about 10 to 1. This chlorobenzal chloride ratio will The separation of the reaction products, both the inter generally result in an orthochlorobenzaldehyde product puri mediate chlorobenzal stage or the final chlorobenzaldehyde ty, after hydrolysis, of about 90 percent and higher. Chlorina stage, into the individual isomers suffers from similar difficul tion to higher ratios of ortho- to para-chlorobenzal chloride is ties as that of the chlorotoluenes. The separation of often desirable when a higher purity product is required and orthochlorobenzal chloride from the product mixture ob 30 ratios of about 20 to 1 and about 50 to l will result in an tained from the side-chain chlorination of a mixture of ortho orthochlorobenzaldehyde product purity of about 95 and and para-chlorotoluene is made particularly difficult by the about 98 percent respectively. The chlorination to a lower possible presence of five additional products, namely, ortho ratio than indicated will result in an increase of the undesira and para-chlorobenzyl chloride, parachlorobenzal chloride ble parachlorobenzaldehyde which is so difficult to separate and ortho- and para-chlorobenzotrichloride, all of which have 35 from its orthoisomer. The chlorination to the degree specified similar vapor pressure curves. also results in the formation of ortho- and para The vapor pressures of ortho- and para-chlorobenzaldehyde chlorobenzatrichloride which upon hydrolysis are converted are again of such similarity as to make separation difficult. At to the corresponding benzoic acids and which can be readily 10 mm., 100 mm., and 760 mm. of mercury pressure, for ex separated as such from the desired orthochlorobenzaldehyde. ample, the boiling points of the orthoisomer are 83, 141 and 40 The relative proportions of the ortho- and para 21 1 C. and of the paraisomer are 90, 147 and 217 C. chlorotoluenes which can be used as starting materials for the respectively. process of this invention can vary considerably without affect It has now been found that orthochlorobenzaldehyde can be ing the usefulness of the process. Generally, to obtain practi cal yields of orthochlorobenzaldehyde, a starting mixture con readily prepared from a starting mixture of ortho- and para 45 chlorotoluene without the use of difficult and costly separa taining at least about 50 percent by weight of tion steps. More specifically it has been found that by orthochlorotoluene should be used. However, a preferred chlorinating the side-chains of a mixture of ortho- and para starting material mixture for this process contains from about chlorotoluene to within certain limits and thereafter hydrolyz 50 to about 85 percent by weight of orthochlorotoluene. A ing the resulting reaction products orthochlorobenzaldehyde 50 starting mixture containing a higher percentage of the can be obtained substantially free from its difficult to separate orthoisomer, while useful in the present process, would no isomer. longer result in a product mixture which suffers from separa The chlorination parameters required to obtain the unex tion difficulties unless very pure products were desired. An pected results of the present invention can be defined in terms orthochlorotoluene content of less than 50 percent by weight of the orthochlorobenzal chloride to parachlorobenzal 55 of the starting mixture results in excessively low yields of chloride ratio in the chlorinated reaction mixture, a procedure orthochlorobenzaldehyde. which is independent of the isomer ratio of the starting materi As previously mentioned, the chlorination step of the als, or in terms of a specific gravity range of the chlorination process of this invention can also be defined in terms of the mixture, a procedure which is dependent on the particular specific gravity of the reaction mixture. It has been found that isomer ratio of the starting materials employed. 60 when an ortho- and para-chlorotoluene mixture containing The process of the present invention and the parameters from about 50 to about 85 percent by weight of the which define its arise from the unexpected chlorination orthoisomer is chlorinated to a corresponding specific gravity products distribution which results when an ortho- and para ranging from at least 1.445 to at least 1.415 respectively at 25° chlorotoluene mixture containing from about 50 to about 85 C. and is subsequently hydrolyzed an orthochlorobenzal percent of the orthoisomer is side chain chlorinated in the 65 dehyde product of at least about 90 percent purity is obtained. liquid phase with chlorine gas. Of particular significance is the The specific gravity used herein is that of the chlorination discovery that under the above conditions as ortho- to para products only and to the exclusion of any solvents or diluents chlorobenzal chloride product weight ratio of at least about 10 which can be used in this process. to 1 and as high as 50 to 1 and higher can be obtained at a time The specific gravity to which the reaction mixture is when the major portion of the orthochlorotoluene has been 70 chlorinated is a function of the particular proportions or converted to the orthochlorobenzalchloride and the compet ortho- and para-chlorotoluenes which is employed as a start ing products, namely, orthochlorobenzal chloride and