Patent GB-758243-A (GB)
Title: Purifying complex esters
Inventor: HOARE MICHAEL FREDERICK
IPC: C07C69/34
Filed: 1952-09-04
Abstract: A crude complex ester containing diester impurities is purified by subjecting the crude ester to extraction with an organic solvent, preferably a hydrocarbon solvent, which dissolves the diesters present but in which the complex ester is substantially insoluble or at least less soluble.  The complex esters are defined as esters containing three or more carboxylic ester groups in a linear arrangement and which are free of olefinic unsaturation, e.g. those formed by the esterification, in one or more stages, of mixtures of a dibasic acid and a dihydric alcohol with a monobasic acid and/or monofunctional alcohol.  The preferred complex esters are those formed by the esterification of dicarboxylic acids, glycols, and monohydric alcohols, either by reacting the three components together or by the monohydric alcohol half ester or glycol half ester method. Specified hydrocarbon solvents are petroleum ether, gasoline, kerosine and light mineral lubricating oil.  The solvent treatment may be carried out by agitating the crude complex ester with the solvent and the extract and raffinate recovered from the two layers formed.  Alternatively, the crude ester can be passed through an extraction tower countercurrent to the solvent and the extract and the raffinate recovered from the streams emerging at either end of the column.  In the case of a hydrocarbon solvent there is a lower limit to the proportion of solvent that may be used to cause separation of the complex ester.  Above this limit increasing the proportion of solvent increases the proportion of precipitated complex ester but there is also an upper limit above which no further complex ester is precipitated.  By control of the quantity and composition of the solvent used it is possible to obtain an upper layer or extract comprising a blend of complex ester and diester to meet a desired viscosity and a raffinate or lower layer comprising purified complex ester.  An example is given for the purification of a crude complex ester prepared from 2 mols. of 2-ethyl hexanol, 2 mols. of sebacic acid and 1 mol. of polyglycol 200 by the glycol half ester method, using petroleum ether as solvent.  The ester is shaken with the solvent and the mixture allowed to stand to form two layers. The upper layer (freed or solvent) comprises the diester, di-2-ethyl hexyl sebacate, together with some complex ester while the lower layer comprises the purified complex ester.  A table is given to show the effect of using various proportions of petroleum ether and petroleum ether-benzole mixtures on the composition of the upper layer.  The extraction can be carried out in more than one stage, e.g. by precipitating in a first stage a high proportion of the complex ester with a large proportion of solvent and then in a second stage precipitating a part of the complex ester from the first stage by using a smaller amount of solvent.  Alternatively, the extract from the first stage may be obtained by using a relatively small amount of solvent and this extract can then be purified by using a greater amount of solvent.  The preferred complex esters for use in the process are those disclosed in Specification 666,697.  It is stated that this ester may be purified by washing with sodium carbonate solution, using petroleum ether as emulsion breaker, and then adding to the separated mixture of petroleum ether and ester an appropriate solvent in accordance with the invention to give an extract of required viscosity.  Specifications 659,103, 662,650 and 707,240 also are referred to.ALSO:In the purification of a crude complex ester containing diester impurities by subjecting the crude ester to extraction with an organic solvent, e.g. a hydrocarbon, which dissolves the diesters present but in which the complex ester is insoluble or at least less soluble (see Group IV(b)), the quantity and composition of the solvent used may be controlled so as to give an extract layer comprising a blend of complex ester and diester of desired viscosity.  The complex esters are defined as esters containing three or more carboxylic ester groups in a linear arrangement and which are free of olefinic unsaturation.  In an example a crude complex ester prepared from 2 moles of 2-ethyl hexanol, 2 moles of sebacic acid and one mole of Polyglycol 200 by the glycol half ester method is shaken with petroleum ether and the mixture allowed to stand to form two layers.  The upper layer (freed of solvent) comprises the diester, 2-ethyl hexyl sebacate, with about 30 per cent complex ester and is stated to be valuable as a lubricant while the lower layer comprises the purified complex ester.  A table is given to show the effect of using various proportions of petroleum ether and petroleum ether-benzole mixtures on the viscosity of the extract.  Other hydrocarbon solvents specified are gasoline, kerosine, and light mineral lubricating oil.  The preferred complex esters are those formed by the esterification of dicarboxylic acids, glycols, and monohydric alcohols.  Specifications 659,103, 662,650, 666,697 and 707,240 [Group IV(b)] are referred to.