Patent GB-574682-A (GB)
Title: New synthetic drying oils and coating compositions
Filed: 1943-06-25
Abstract: Glycerol mixed esters of one or more monofunctional a  : b -ethylenic-b -aryl monocarboxylic acids, as hereinafter defined, and at least one other monofunctional aliphatic monocarboxylic acid of different structure may be used as synthetic drying oils and may replace the rapidly drying natural fatty oils which are normally formulated in coating compositions.  The a  : b -unsaturated acid is any monocarboxylic acid having an ethylenic double bond between the a - and b -carbon atoms and an aromatic ring directly attached to the b -carbon atom; the remainder of the molecule is substantially immaterial provided the acid contains no groups such as hydroxyl, amino or sulphhydryl which are known to react with the carboxyl group under normal esterification conditions, i.e. the acid is "monofunctional," and there be no alken-l-yl group attached to the a -carbon atom and no thienyl group attached to the a - or b -carbon atoms; otherwise the acid may be saturated or unsaturated and substituted or not by such inert groups as ether, ketone, halogen or sulphide.  The following acids are specified: cinnamic acid, p-methoxy cinnamic acid, 3 : 4-methylenedioxy-cinnamic acid, b -(a -naphthyl) acrylic acid, a -bromocinnamic acid, b -methyl cinnamic acid, a  - methyl - cinnamic acid, 3 : 4 - dimethoxy - cinnamic acid, and b -phenyl cinnamic acid.  The monofunctional aliphatic monocarboxylic acids may be saturated or unsaturated, straight or branched chain and substituted or not by such non-reactive groups as ether, ketone or halogen; preferably they are unsaturated and those derived from drying or semi-drying oils are most useful.  The acids specified include linseed oil, perilla oil, oiticica oil, chinawood oil, soya bean oil, corn oil, cottonseed oil and coconut oil acids, oleic acid, stearic acid, lauric acid, butyric acid, crotonic acid and sorbic acid.  The glycerol mixed esters may be prepared by reacting the a  : b -ethylenic-b -aryl carboxylic acid with a glycerol partial ester of the other acid of different structure. The partial ester is suitably prepared by heating a fatty oil and glycerol together with an alcoholysis catalyst, such as litharge, the proportions employed being calculated to give the desired degree of alcoholysis; the heating is carried out in an oxygen-free inert atmosphere such as of carbon dioxide or nitrogen.  The partial ester so obtained is heated with an amount of the a  : b -unsaturated acid sufficient to esterify the free hydroxyl groups in the presence of a hydrocarbon solvent.  The distilling vapours of solvent and water of esterification are condensed and the solvent returned to the reaction in a continuous manner.  Aromatic hydrocarbons, chlorinated solvents, ethers and ketones are suitable solvents, those mentioned specifically being toluene, xylene, cymene, amylbenzene, tetrachlorethane, anisol and cyclohexanone.  A viscous solution of the mixed ester results from which, if desired, the solvent may be removed by distillation or blowing with carbon dioxide.  This process may also be carried out in the absence of a solvent.  An esterification catalyst such as sodium bisulphate may be included. The mixed esters can also be made by reacting glycerol simultaneously or successively, in any order, with the a  : b -unsaturated acid or acids and other monocarboxylic acid or acids; alternatively, a glycerol simple ester of either acid may be reacted successively with additional glycerol and the remaining acid, the alcoholysis step being carried out preferably with the aid of an alcoholysis catalyst such as litharge, sodium hydroxide or sodium alcoholate suitably in amount from 0.01 to 1.0 per cent.  Esterifiable derivatives of the acids may be employed in these processes such as the anhydrides, acid halides and esters of alcohols more volatile than glycerol.  The preferred glycerol mixed esters, especially those of cinnamic acid and drying or semi-drying oils, contain the equivalent of 10 to 30 per cent of a  : b -ethylenic-b -aryl monocarboxylic acid glyceride. The desired proportion is normally obtained by using the calculated amount of a  : b -unsaturated acid, but a mixed ester of similar effect is obtained by preparing a mixed ester of higher a  : b -unsaturated acid glyceride content than is desired and blending it with the drying oil whose acids are being used (or, if desired, a different oil) in an amount calculated to give the required a  : b -unsaturated acid glyceride content, and if this glyceride content is initially high (say, above 25 per cent), the blending is preferably carried out at elevated temperatures.  According to examples: (1) a partial glycerol ester prepared by reacting linseed oil and glycerol to give the diglyceride, is refluxed with cinnamic acid and toluene in a carbon dioxide atmosphere, the distilling vapours of toluene and water of esterification being condensed and the toluene returned to the reaction; at the end of the reaction the solvent is removed from the product by vigorous blowing of the reaction mixture with carbon dioxide.  Films of the resultant mixed ester oil containing 0.03 per cent cobalt drier (added as cobalt naphthenate) are tack-free on standing overnight.  Faster drying is obtained by baking, with or without driers.  A resin-oil varnish may be formulated by bodying the oil by heating in a carbon dioxide atmosphere, adding a limed rosin solution (in mineral spirits) and manganese resinate and lead naphthenate, and finally diluting with mineral spirits.  The oil may also be made into an enamel by milling a mixture of the oil, titanium dioxide, antimony oxide and a hydrocarbon thinner and adding cobalt and lead driers; (2) a glycerol mixed ester is obtained from linseed oil diglyceride and p-methoxy cinnamic acid (itself prepared by reacting p-methoxybenzaldehyde acetic anhydried and sodium acetate according to Perkin's method) by the method described in the preceding example; this oil with 0.03 per cent cobalt gives dust and tack-free films; (3) a glycerol mixed ester of linseed oil acids and 3 : 4-methylenedioxycinnamic acid is prepared similarly and with 0.03 per cent cobalt also gives tack-free films; the 3 : 4-methylene-dioxy cinnamic acid is prepared by condensing 3 : 4-methylenedioxybenzaldehyde with malonic acid; (4) linseed oil diglyceride prepared as in example (1), but using litharge as an interchange catalyst, is reacted with b -(a -naphthyl) acrylic acid (itself prepared from a -naphthaldehyde, methyl acetate and sodium methoxide) as in the previous examples, and this mixed ester oil also gives tack-free films with 0.03 per cent cobalt.  The glycerol mixed esters may be used alone or in blends with copal, kauri, ester-gum, oil-soluble and rosin-extended phenol-formaldehyde resins, such as "Amberols," vinyl or urea-formaldehyde resins, cellulose derivatives such as nitrocellulose, cellulose acetate or aceto-propionate and ethyl cellulose, waxes, solvents, pigments, plasticizers and particularly with fatty oils, especially drying or semi-drying oils, preferably by hot blending.  These compositions may be applied to wood, metal, paper, linen, silk, cotton and regenerated cellulose wrapping foils.  Specific manufactures mentioned are linoleum, patent leather, linoxyn-type materials, coated copper wire, oiled cloth and silk, printing inks and sandpaper; the esters may also be used in moulding compositions and putties, and as modifying agents for urea- and phenol-formaldehyde resins.  Specification 569,404 is referred to.  The Specification as open to inspection under Sect. 91 comprises also the preparation of mixed esters from polyhydric alcohols in general, and ethylene glycol, diethylene glycol, triethylene glycol, hexamethylene glycol, tetramethylene glycol, erythritol, pentaerythritol, sorbitol, mannitol, cyclohexyl-1 : 2-dicarbinol, methyltrimethylolmethane, and p : p1-di-(2-hydroxyethyl) benzene are specified.  The monofunctional monocarboxylic acids may be aromatic or aliphatic, open or closed chain and, if the latter, mono-, poly-, homo-, or heterocyclic and in addition to those given above, p-toluic acid, benzoic acid, furoic acid, quinolinic acdd, a  - naphthionic acid and phenoxyacetic acid are specified.  The mono-functional a  : b -unsaturated acids may contain aromatic or aliphatic, open or closed chain radicals and, if the latter, homo- or hetero-cyclic radicals; but no further examples are given.  It is stated that the mixed esters may also be prepared by heating together a polyhydric alcohol, a polyhydric alcohol ester such as a drying or semi-drying oil and sufficient of the a  : b -ethylenic-b -aryl monocarboxylic acid to esterify the free hydroxyl groups present in this mixture. This subject-matter does not appear in the Specification as accepted.