Reissued Nov. 18, 1952 Re. 23,584 UNITED STATES PATENT oFFICE 28,584 MANUFACTURE OF PENTAERYTER OL Harry Jackson, Stevenston, and Griffith Glyn Jones, Annan, Scotland, assignors to imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Original No. 2,562,102, dated July 24, 1951. Serial No. 695,050, September 5, 1946. Application for reissue December 3, 1951, Serial No. 259,698. In Great Britain September 1, 1945 2 Claims. (CL 260-635) Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue. 1. 2 The present invention is concerned with a new and calcium formate if there are present 4 moles and improved process for the manufacture of formaldehyde and 0.5 mole calcium hydroxide pentaerythritol by means of the well known re per mole acetaldehyde. When the theoretical action that occurs between acetaldehyde and quantities of the reagents are present, the fact formaldehyde in aqueous solution in presence of that the formaldehyde and the lime are partly a strong base such as calcium hydroxide. consumed in the formation of the aforesaid by In the earlier preparations of pentaerythritol products implies that there will be insufficient to described in the literature the tWO aldehydes Were react with the whole of the acetaldehyde to form caused to react in presence of the base at very pentaerythritol. With the object of minimising high dilutions over long periods of time, so that O the loss occasioned by formation of these by they were not well adapted for commercial pro products, it is usual to employ somewhat more duction. In the processes that have been en than the theoretical proportions of formaldehyde ployed commercially for the production of penta and lime, for instance 4.5 moles formaldehyde per erythrito, the aldehydes are used in considerably mole acetaldehyde, and at least sufficient calcium higher concentrations, the acetaldehyde concen 5 hydroxide to leave some undissolved lime after tration usually exceeding one mole for every 80 the reaction is over. moles water, and the temperatures are such that When a reaction mixture, in which acetalde the alkaline condensation is completed in the hyde is gradually added to a mixture of lime and course of an hour or two or even less. The alkali formaldehyde Solution in excess as aforesaid, has most commonly used is line; and after the 20 been allowed to warm up during the early stages alkaline condensation is over a precipitant for of the reaction and is maintained at a suitable the calcium formate and other soluble calcium. temperature during the addition of the acetalde compounds present in the resulting Solution is hyde, there is a tendency for a further rise in the introduced, and the clear liquor is evaporated temperature to take place spontaneously after the down under reduced pressure until crude penta 25 acetaldehyde has all been added. It has hitherto erythritol can be crystallised from it. The pre been the practice, in order to ensure the comple cipitation of the calcium compounds is commonly tion of the desired reaction after the ingredients carried out by acidifying the solution with sul Of the reaction mixture have all been introduced phuric acid in amount sufficient to convert them to permit the temperature to rise to a point just into calcium sulphate, most of which settles out, short of the point at which a dark yellow or brown the clear liquor being further treated for the 30 colour develops, and to keep the reaction mixture conversion of the calcium Sulphate remaining in stirred until the falling aldehyde concentration the solution into insoluble compounds or partly of the Solution shows no further tendency to di into insoluble compounds and partly into soluble minish. This temperature may be anything from compounds that will not deposit during the about 45 C. to 63 C. according to the manner evaporation. in which the reaction is carried out. Figures It is well known that troublesome by-products have been published by Friedrich and Braun are formed in the reaction mixture. These troublesome by-products include Syrupy products (Berichte 1930, LXIII, page 2687) indicating that resulting from self-condensation of formaldehyde when one half mole of lime is used per mole in presence of the base, and also dipentaerythritol. 40 acetaldehyde and the reaction mixture is heated It has also been stated that tripentaerythritol at the end to 45° C., the ratio of pentaerythritol which, like dipentaerythritol, is a polyhydroxy to other compounds in the crude pentaerythrito compound but contains two ether groups instead is at a maximum when five moles formaldehyde of one, is formed. Both the syrupy self-conden are used per mole acetaldehyde. sation products of formaldehyde and the poly It is an object of the present invention to in pentaerythritols interfere with the recovery of the prove the ratio of the amount of pentaerythritol pentaerythritol. The syrupy products, however, to the amount of other products formed in the are easily soluble in alcohol and can be removed reaction, and especially to improve the ratio of from the crude pentaerythritol much more easily pentaerythritol to poly-pentaerythritols in the than can the crystalline poly-pentaerythritols, crude crystallised pentaerythritol so that penta from which it is especially difficult to separate the erythritol of improved purity may be obtained. pure pentaerythritol, even by recrystallisation. A further object is to provide a process suitable It should theoretically be possible to achieve for commercial application wherein an improved the complete conversion of the reagents in the yield of pentaerythritol of high quality is ob alkaline reaction mixture into pentaerythritol 55 tained, . 88,584 3 4. The present invention is based in part on the maining in solution into barium sulphate and observation that, when the condensation is calcium formate, further filtration and evapora carried out in presence of an excess over the tion under reduced pressure, theoretical amount of the alkaline material sun In putting the invention into effect, the amount client to leave an excess on the disappearance of of formaldehyde employed in the reaction mix the acetaldehyde, the employment of increasingly ture per mole acetaldehyde may range from 5 to large excesses of formaldehyde over the theoreti about 10 moles, or even more, and is preferably cal quantity reckoned on the acetaldehyde, at least 7 moles. The amount of the line should ranging from about 5 to 10 or even more moles preferably be sufficient to leave an undissolved per mole acetaldehyde results in a progressive 0 excess at the end of the reaction. Preferably the reduction in the amount of the dipentaerythritol formaldehyde solution and the calcium hydroxide or other by-products formed in the reaction that are mixed together and the acetaldehyde, desira crystallises from the concentrated liquors with bly in aqueous solution, is gradually added to the the pentaerythritol and that in part on the ob mixture with agitation. Except that during the servation that if the customary heating at the 5 admixture of the reagents and during the sub end of the reaction is omitted and the tempera sequent period while the mixture is kept agitated ture of the alkaline reaction mixture is never al until the acetaldehyde is consumed the tempera lowed to exceed 33 C., and the reaction is inter ture must be rigorously controlled so that it never rupted whenever the acetaldehyde has been con exceeds 33 C. and apart from the preferably high sumed, any such amounts of formaldehyde may 20 proportion of formaldehyde used the conduct of be employed without giving rise to any extensive the condensation reaction according to the pres formation of syrupy formaldehyde alkaline con ent invention need present no special feature. An densation products and can be easily removed incidental advantage of the lower maximum tem and largely recovered so that pentaerythritol of peratures to which the reaction mixture is sub high quality may be obtained in improved yield. 25 jected lies in the fact that they tend to minimise According to the present invention, a process the losses occasioned by volatilisation of the acet for the manufacture of pentaerythritol by the aldehyde, and this can only be advantageous to interaction of formaldehyde and acetaldehyde in the yield of pentaerythritol-obtained. If desired the presence of a strongly basic hydroxide con the cooled alkaline reaction mixture may be prises the employment of a considerable excess 30 filtered or decanted away from the undissolved of formaldehyde Over the theoretical reckoned on portion of the excess of lime before the liquor is the acetaldehyde and a quantity of said hydroxide treated with acid used to convert the free lime exceeding the theoretical amount sufficient to present in it or calcium salt, for instance sul leave an excess on the disappearance of the acet phuric acid, sufficient of the acid being employed aldehyde, maintaining the alkaline reaction mix to confer a faint permanent formic acid acidity ture at a temperature not exceeding 33 until the on the liquor. Methyl Red may be used at this disappearance of the acetaldehyde and thereupon, stage to indicate by a change in colour from still at a temperature not exceeding 33 C., re yellow to red when sufficient acid has been added. moving its free alkalinity. When Sulphuric acid is used the precipitated After the free alkalinity of the reaction mixture 40 calcium sulphate is preferably removed, for in has been removed by adding sufficient of an acid stance by filtration. Acids yielding easily soluble to render the solution only slightly acid to an in calcium salts may however be used instead of sul dicator changing colour at about the same acidity phuric acid, for instance formic acid, and in this fas Methyl Red the unreacted excess of formal case the whole of the free line dissolves up and dehyde may be stripped from the reaction mix filtration is rendered unnecessary at this stage.