Patent GB-704943-A (GB)
Title: Improvements in and relating to the dehydrogenation of alcohols
IPC: C07C45/00
Filed: 1950-12-15
Abstract: A continuous process for the dehydrogenation of alcohols to produce the corresponding aldehydes or ketones comprises continuously feeding the alcohol to a reactor containing a boiling mixture comprising the alcohol and a solid dehydrogenation catalyst, the pressure being preferably atmospheric but if necessary above or below atmospheric, the vaporous product from the reactor being immediately passed to a fractionating column, unreacted alcohol and/or other material which leaves the reactor in the form of vapour together with the aldehyde or ketone being refluxed to the reaction zone, and the final aldehyde or ketone product being recovered by condensing the vapour leaving the top of the column.  The invention also comprises as new compounds: 4, 5, 5-trimethyl-hexanal-1; 3, 4, 5-trimethyl-hexanal-1, and 3, 4, 4-trimethyl-hexanal-1.  The process is particularly applicable to alcohols boiling between 150 DEG C. and 250 DEG C. and especially to branch chain alcohols, e.g. OXO alcohols.  When the process is applied to alcohols boiling above 250 DEG C. the dehydrogenation temperature is modified either by reducing the pressure or by using an entrainer for the aldehyde or ketone product, the entrainer having a boiling point lower than that of the alcohol and being preferably one which forms an azeotrope with the dehydrogenation product which on condensation separates into two layers, one rich in entrainer, the entrainer or entrainer-rich layer being returned continuously to the boiler.  Suitable entrainers are the paraffinic and aromatic hydrocarbons and their chlorinated derivatives.  The process is also applicable to low boiling alcohols (boiling point below 150 DEG C.) by the use of increased pressure and in this case, as well as in general, the tendency to rehydrogenation may be minimized by separating hydrogen from the reaction zone at the bottom of the fractionating column by means of selective diffusion. The invention is applicable to aliphatic alcohols and to primary and secondary cyclic alcohols.  In examples: (1) 3, 5, 5-trimethyl-hexanal-1 is obtained from the corresponding nonanol by feeding the nonanol to a unit comprising a reactor/boiler on which is mounted a specially designed column packed with stainless steel gauze rings so as to give a high aldehyde content in the product taken-off and a low concentration of aldehyde in the reflux return to the reactor. The process is operated continuously at 190 DEG  to 260 DEG C. and the catalyst used is a copper barium chromite catalyst prepared by thermal decomposition of the precipitate obtained by adding ammonia to a solution containing copper nitrate, barium nitrate and chromium trioxide and the catalyst is used in a concentration of 5 per cent. by volume in the alcohol-catalyst mixture; (2) 4, 5, 5-trimethyl hexanol-1; 3, 4, 5-trimethyl-hexanol-1, and 3, 4, 4-trimethyl-hexanol-1 are obtained by dehydrogenation of the corresponding nonanols, the initial reaction temperatures being 202.0 DEG C., 205.5 DEG C., and 207.5 DEG C. respectively and the same catalyst being used as in (1).  The properties of these aldehydes and of their 2, 4-dinitrophenyl hydrazones are tabulated; (3) heptanol-1, octanol-1, and decanol-1 are obtained from the corresponding aldehydes by dehydrogenation at 175 DEG C., 196 DEG C. and 231 DEG C. respectively using the same catalyst as in (1); (4) and (5) hexahydrobenzaldehyde and a mixture of isomeric dimethylcyclohexanones are obtained by dehydrogenation, using the same catalyst as above, of cyclohexyl carbinol and a mixture of isomeric dimethylcyclohexanols respectively, the latter being obtained by hydrogenation of commercial cresylic acid; (6) furil is obtained by dehydrogenation of furoin the product being entrained in and separated at about 200 DEG C. from a refluxing solution in a high molecular weight hydrocarbon such as pentamethylheptane obtained by hydrogenating trimerized isobutene.ALSO:In a continuous process for the dehydrogenation of alcohols to produce aldehydes or ketones (see Group IV (b)) by continuously feeding the alcohol to a reactor containing a boiling mixture comprising the alcohol and a solid dehydrogenation catalyst, the vapours produced are passed to a fractionating column from which unreacted alcohol and/or other material is refluxed to the reaction while the aldehyde or ketone products are recovered by condensing the vapours leaving the top of the column.  When the process is applied to alcohols boiling above 250 DEG C. the dehydrogenation temperature is modified either by reducing the pressure or by using an entrainer having a boiling point lower than that of the alcohol and being preferably one which forms an azeotrope with the dehydrogenation product which on condensation separates into two layers, one rich in entrainer, the entrainer or entrainer rich layer being returned continuously to the boiler. Suitable entrainers are the paraffinic and aromatic hydrocarbons and their chlorinated derivatives.  In an example furil is obtained by dehydrogenation of furoin using copper barium chromite as dehydrogenation catalyst, the product being entrained in and separated at, about 200 DEG C. from a refluxing solution in a high molecular weight hydrocarbon such as pentamethylheptane.