Patent GB-574681-A (GB)
Title: New synthetic drying oils and coating compositions
Filed: 1943-06-25
Abstract: Glycerol esters of one or more acylacrylic monofunctional monocarboxylic acids and, if desired, one or more monofunctional aliphatic monocarboxylic acids of different structure, may be used as synthetic drying oils and can be substituted for the rapidly drying natural fatty oils normally formulated in coating compositions. These glycerol esters may be simple esters in which all the hydroxyl groups of the glycerol are esterified with the one and same acylacrylic acid, or may be mixed esters in which the hydroxyls are esterified with different acylacrylic acids or with an acylacrylic acid and one or more monofunctional aliphatic monocarboxylic acids of different structure.  The acylacrylic acids are those keto-monocarboxylic acids having an ethylenic double bond between the a - and b -carbon atoms and an acyl group attached to either the a - or b -carbon.  The remainder of the molecule is substantially immaterial provided there are no groups, for example, hydroxyl, primary or secondary amino, or sulphhydryl groups, known to react with carboxyl groups under normal esterification conditions and further, that there be no aryl group attached to the b -carbon and no thienyl group attached to the a - or b -carbon atoms; other non-reactive substituent radicals may be present, saturated or unsaturated and substituted or not by inert groups such as ether, ketone, halogen, or sulphide.  The aliphatic monocarboxylic acids of different structure may be saturated or unsaturated, straight or branched chain and substituted or not by non-reactive groups or atoms such as ether, ketone or halogen, and are preferably unsaturated, the acids of natural drying or semi-drying oils being most useful; examples are the acids from perilla oil, oiticica oil, chinawood oil, dehydrated castor oil, soya bean oil, corn oil, cottonseed oil and coconut oil, and oleic, lauric, stearic, butyric, crotonic and sorbic acids.  The glycerol simple esters are prepared by reacting glycerol with the acylacrylic acid or an esterifiable derivative such as the acid anhydride or halide or ester with an alcohol more volatile than glycerol, one or more of the alcoholic hydroxyls being esterified. The mixed esters are prepared in general by reacting glycerol simultaneously or successively, in either order, with the several acids or their esterifiable derivatives.  The free a -acylacrylic acids are generally unstable and are preferably employed in the form of an ester of an alcohol more volatile than glycerol.  In one method of preparing mixed esters the acylacrylic acid or ester thereof with a volatile alcohol is reacted with a glycerol partially esterified with the different monocarboxylic acid.  The partial ester is prepared by heating glycerol and fatty oil in proportions calculated to give the desired degree of alcoholysis, in the presence of an alcoholysis catalyst such as litharge and in the presence of an oxygen-free inert gas such as carbon dioxide or nitrogen, and then is added the acylacrylic acid or esterifiable derivative in amount sufficient to esterify the remaining hydroxyl groups, with a hydrocarbon solvent such as xylene or toluene.  The distilling vapours of solvent and water of esterification are condensed and the solvent returned to the reaction in a continuous manner.  An esterification catalyst such as sodium bisulphate may be present. A viscous solution of the mixed ester is obtained from which the solvent may be removed, if desired, by distillation or blowing with carbon dioxide.  Alternatively, a glycerol simple ester of either acid can be reacted successively with additional glycerol and the remaining acid, the alcoholysis being carried out in the presence of a catalyst such as litharge sodium hydroxide or sodium alcoholate. Other solvents may be used in the above-described solution method such as cymene amylbenzene, tetrachlorethane, anisol and cyclohexanone; in general, aromatic hydrocarbons, chlorinated solvents, ethers and ketones are suitable.  It is stated that this process may also be carried out in the absence of a solvent. Light-coloured products are obtained by reacting at low temperatures in the absence of oxygen and by avoiding the use of materials which liberate oxygen in the reaction.  Preferably, the glycerol mixed esters contain the equivalent of 10-40 per cent of b -acylacrylic acid glyceride.  This desired proportion is normally obtained by using the calculated amount of acylacrylic acid, but a similar product may be obtained by preparing a mixed ester of greater b -acylacrylic acid glyceride content than is desired and blending therewith sufficient of the drying oil whose acids are being used (or, if desired, a different oil) in an amount calculated to give the desired acylacrylic acid glyceride content, employing elevated temperatures if the initial acrylic acid glyceride content is high, say, above 25 per cent.  The esters may be formulated into coating composition either alone, or with copal, kauri, ester-gum, oil-soluble and rosin-extended phenol-formaldehyde resins, vinyl or urea-formaldehyde resins, nitrocellulose, cellulose acetate or aceto-propionate, ethyl cellulose, waxes, solvents, pigments and 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 being linoleum, patent leather, linoxyn-type materials, coated copper wire, oiled cloth and silk, printing inks, sandpaper, moulding compositions and putties.  In addition, they may be used as modifying agents for urea- and phenol-formaldehyde resins.  In examples: (1) a glycerol mixed ester is prepared from linseed oil acids and b -benzoylacrylic acid by the solution method described above. The ester oil dries to a hard tack-free film; it may be formulated into a varnish by mixing the heat-bodies oil with an "Amberol" rosin and lime, diluting the clear solution with a hydrocarbon thinner and adding lead naphthenate and manganese resinate driers; an enamel is prepared by milling a mixture of the ester oil, titanium and antimony oxides and a hydrocarbon thinner and then adding cobalt and lead driers; (2) a glycerol mixed ester of linseed oil acids and b -(2 : 4-dimethylbenzoyl) acrylic acid prepared as in (1) above, also gives tack-free films with 0.03 per cent cobalt; the benzoylacrylic acid is prepared from xylene and maleic anhydride; (3) a glycerol mixed ester of linseed oil acids and a -acetocrotonic acid is prepared by heating methyl a -acetocrotonate (itself prepared by condensing acetaldehyde with methyl acetoacetate in the presence of hydrogen chloride) with glycerol using litharge as alcoholysis catalyst and reacting the product with linseed oil and linseed oil acids according to the solution method.  The mixed ester with 0.03 per cent cobalt dries tack free; (4) a glycerol mixed ester of linseed oil acids and a -aceto-b -(2-furyl) acrylic acid is prepared as in the preceding example, using methyl a -aceto-b -(2-furyl) acrylate, which is itself prepared by condensing furfural and methyl acetoacetate with piperidine as catalyst; (5) a glycerol mixed ester of linseed oil acids and 2-aceto-5-phenyl pentadien-2 : 4-oic acid is also p  prepared as in (3) above using methyl 2-aceto-5-phenylpentadien 2 : 4-oate obtained by condensing cinnamaldehyde and methyl acetoacetate with piperidine as catalyst; (6) a glycerol mixed ester is prepared according to the solution method from linseed oil diglyceride and ethyl a -aceto-b -(2-furyl) acrylate; (7) a glycerol mixed ester is similarly prepared from a linseed oil diglyceride and b -dibenzofuroylacrylic acid using sodium bisulphate as catalyst; the dibenzofuroyl acrylic acid is prepared by reacting dibenzofurane and maleic anhydride in carbon disulphide in the presence of aluminium chloride.  All these esters give tackfree films when 0.03 per cent cobalt drier is added.  Other acylacrylic acids employable are b -(2-naphthoyl) acrylic acid, b -(4-methoxy-benzoyl) acrylic acid, and b  - benzoyl - a  : b  - dimethylacryli acid, prepared respectively from naphthalene and maleic anhydride, from anisole and maleic anhydride, and from benzene and dimethylmaleic anhydride according to the general method of Pechmann; b -acetylacrylic acid and a -benzoylacrylic acid prepared respectively from aldehyde and methyl acetate and from benzaldehyde and methyl aceto-acetate by condensation in the presence of hydrogen chloride; and 4-ketoheptadien-2 : 5-oic acid, a -acetosorbic acid, and a -acetoacrylic acid prepared respectively from the aldehyde of formula CH3CH=CHCOCHO,-itself obtainable by Claisen condensation of acetaldehyde and pyruvic aldehyde-and acetic acid, from crotonic aldehyde and acetoacetic acid and from formaldehyde and acetoacetic acid, all by the general method of Perkin.  Specification 569,404 is referred to.  The Specification as open to inspection under Sect. 91 describes also the preparation of esters of other polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, tetramethylene glycol, hexamethylene glycol, mannitol, sorbitol, cyclohexyl-1 : 2-dicarbinol, methyltrimethylolmethane, and p : p - di - (2 - hydroxyethyl) benzene.  The monocarboxylic acids of different structure may be aromatic or aliphatic; open or closed chain, and if the latter, mono-, poly-, homo- or hetero-cyclic; additional examples are p-toluic acid, benzoic acid, furoic acid, quinolinic acid, a -naphthionic acid, and phenoxy-acetic acid. The acylacrylic acids may contain aromatic or aliphatic, open or closed chain radicals including homo- and hetero-cyclic radicals. An additional method of preparing the mixed esters comprises heating together a polyhydric alcohol, a polyhydric alcohol ester such as a drying or semi-drying oil and sufficient acylacrylic acid or