IE913719A1 - Process for the preparation of aldehydes from¹ó-trihalogenated secondary alcohols - Google Patents

Abstract

The characteristic of the process of the invention consists in performing the scission reaction of the alpha -trihalogenated secondary alcohol to the corresponding aldehyde and trihalomethane in a weakly or moderately polar solvent and in the presence of a catalyst which is a salt with basic properties, insoluble in the reaction mixture.

Description

PROCESS, FOR THE PREEAKATION OF ALDEHYDES FROM a-TRIHALOGENATED SECONDARY ALCOHOLS The present invention relates to a process for the preparation of aldehydes from a-trihalogenated secondary alcohols or trihalomethylcarbinols. α-Trihalogenated secondary alcohols are known products, and various processes for converting these compounds either into e-hydroxy acids or into aldehydes are described in the state of the art.

Patent FR-A 583,856 to Aktiengesellschaft ftir Anilin Fabrikation describes a process for the preparation of vanillin (3-methoxy-4-hydroxybenzaldehyde) from 3- methoxy-4-hydroxyphenyltrichloromethylcarbinol by heating under reflux in aqueous solution in the presence of large quantities of copper acetate.

Such a preparation is lengthy (generally 12 hours) and requires prohibitive quantities of copper acetate, and this makes the process costly and not adaptable to an industrial scale. Furthermore, high dilutions are involved in the operation.

Patent FR-A 727,165 to I.G. Farbenindustrie describes another process for the scission of 3-methoxy4- hydroxyphenyltrichlororaethylcarbinol and 3-ethoxy4-hydroxyphenyltrichloroaethylcarbinol resulting in the corresponding aldehydes. The said process consists in treating the said phenyltrichoromethylcarbinols with an alkali metal alcoholate or an alkali or alkaline-earth metal alcoholic hydrate in methanol, under reflux. Aldehyde yields of approximately 50 to 75% are thus obtained, but the isolation of this product requires a lengthy sequence of operations: treatment with an acid to release the aldehyde obtained in phenate form, removal of the solvent, extraction with chloroform and then distillation of the aldehyde.

According to patent FR-A 791,818 to Rhone-Poulenc and its certificates of addition FR-A 46,789 and FR-A 47,291, a process for the preparation of aldehydes from aryltrichloromethylcarbinols has also been proposed, - 2 which consists in performing the saponification and the oxidation of aryltrichloromethylcarbinole with an alkaline aqueous solution, at boiling point (or at a higher temperature), of an alkali or alkaline-earth metal chromate, manganese dioxide, lead dioxide, barium peroxide, aqueous hydrogen peroxide or alkali metal perborate or persulfate, optionally in the presence of metallic copper.

According to this process, the operation must be carried 10 out in a very dilute medium and reaction byproducts are formed, which must then be separated from the reaction mixture.

Another process referred to in patent GB-A 453,482 to Monsanto Chemicals Limited consists in preparing alkoxyhydroxybenzaldehydes by oxidation of the corresponding alkoxyhydroxyphenylglycolic acid by heating in an aqueous solution of an alkali metal hydroxide in the presence of an aromatic nitro compound such as nitrobenzene, m-dinitrobenzene or m-nitrotoluene. The said glycolic acid is obtained by hydrolysis of the corresponding phenyltrichloromethylcarbinol.

More recently, patent FR-A 2,244,743 to Shell international Research Maatschappij B.V. describes the synthesis of hydroxybenzaldehydes by scission of tri25 chloromethylcarbinols in polar aprotic solvents in the presence of a base chosen from alkali or alkaline-earth metal hydrides, alcoholates or carbonates. The reaction time remains quite long (4 to 24 hours). The treatment for recovering the aldehydes obtained is not easy, especially since the necessary acidification in an aqueous medium loads to difficulties in the subsequent separation of the polar aprotic solvent from water if the intention is not to waste largo quantities of these costly solvents. Patent application EP-A 44,009 by Bayer describes [3-hydroxy-4-(2,2,2-trichloro-l-hydroxyethyl)]1-phenyl-1,2,3**triazoles as new compounds and points out that they can be converted into the corresponding aldehydes by the action of an alkali or an alkaline-earth metal hydroxide or alcoholate in a polar aprotic medium. - 3 The operation of isolating the aldehyde obtained from the reaction mixture presents the same problems as in the case of the preceding process.

One characteristic which is common to all these 5 processes is that they are not adapted to compounds other than the hydroxyphenyltrichloromethylcarbinol derivatives. It appears that the presence of the phenol functional group is necessary. In addition, the operations for isolating the aldehydes obtained from the reaction mixture are relatively lengthy and complex.

An objective of the invention is therefore to provide a very general process for obtaining aldehydes from α-trihalogenated secondary alcohols corresponding to the general formula (I) Q-CH-CX3 (I) OH in the said formula, Q denotes an optionally substituted, monovalent hydrocarbon radical containing from 1 to 40 carbon atoms and X symbolises a halogen atom, chlorine, fluorine, bromine or iodine and, preferably, chlorine.

In formula (I), the group -CH-CX3 will be called OH a trihalomethylcarbinol.

The characteristic of the process of the inven25 tion consists in performing the scission of the α-trihalogenated secondary alcohols into the corresponding aldehydes and trihalomethanes in a slightly or moderately polar aprotic solvent and in the presence of a catalyst which is a salt with basic properties and which is insoluble in the reaction mixture. in the description of the present Invention which follows, a slightly or moderately polar aprotic solvent means a solvent which does not contain groups of the GaXH type; in the said formula: - G symbolises a saturated or unsaturated aliphatic hydrocarbon radical containing from l to 4 A aromatic cyclic radical containing 5 or 6 atoms/ - denotes 0, S, COO, CSS, COS, SO, or P03 when a “ 1 and X denotes N or P when a = 2.

A salt with basic properties also denotes a salt whose anion has a pK^ in aqueous medium at 25*C of between 0 and 14 and preferably between 0 and 11, and still more preferably between 0 and 8. pKb is defined according to the well-known equations 10 pK„ - 14 - pKa, pK. being the cologarithm of the dissociation constant of the acid in aqueous medium.

In accordance with the process of the invention, the scission reaction of the α-trihalogenated secondary alcohol corresponding to the formula (I) takes place according to the general equation: suitable solvent Q-CH-CX, _> Q-C-H + CHX, J catalyst | OH O The process of the invention is characterised in that the scission reaction of the trihalomethylcarbinol takes place in a solid-liquid, heterogeneous catalyst system. The catalyst is in suspension in a liquid phase comprising the trihalomethylcarbinol and the organic solvent.

Such a catalyst system makes it possible to obtain a very good conversion of the trihaloaethylcarbinol and a very good reaction selectivity. As a result, the aldehyde is obtained in an excellent yield..

Another advantage of the process of the invention is the ease of recovery of the aldehyde formed and of the catalyst, since the reaction takes place in a heterogeneous phase.

Finally, a further positive feature of the process of the invention is that it allows an aldehyde to be prepared without any contaminating effluent, since the trihalomethane formed can be reclaimed.

More .precisely, the β-trihalogenated secondary - 5 alcohols ot trihalomethylcarbinols used as starting materials for the preparation of the aldehydes correspond to the general formula (I) in which Q denotes a monovalent hydrocarbonyl radical, substituted or not, which may be a linear or branched, saturated or unsaturated acyclic aliphatic radical or a monocyclic or polycyclic, saturated, unsaturated or aromatic carbocyclic or heterocyclic radical.

Trihalomethylcarbinols of general formula (I) in which Q denotes a monocyclic or polycyclic aromatic hydrocarbon radical are very particularly suitable for the application of the process of the invention; the radicals may together form orthocondensed or ortho- and pericondensed systems. More particularly, the naphthyl radical may be mentioned.

Q preferably denotes an aryl radical corresponding to the general formula (II)s In the said formula (II): - n is an integer from 0 to 5, preferably from 0 to 3, - R denotes Rx, one of the following groups or functional groups i - a linear or branched alkyl radical containing from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl or tert^ butyl, - a linear or branched alkenyl radical containing from 2 to 6 carbon atoms, preferably from 2 to 4 carbon atoms, such as vinyl or allyl, - a linear or branched alkoxy radical containing from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms, such as the methoxy, ethoxy, propoxy, isopropoxy and butoxy radicals, - 6 10 - a radical of formula -R2-OH -r2-cooh -Ra-CHO -R2-NO2 -r2-cn -r2-nh2 -r2-sh -r2-x -r2-cf3 In the said formulae, R2 denotes a valency bond or a saturated or unsaturated, linear or branched divalent hydrocarbon radical containing from 1 to 4 carbon atoms, such as, for example, methylene, ethylene, propylene, isopropylene or isopropylidene, and X symbolises a halogen atom, especially a chlorine or bromine atom.

- R denotes R3, one of the following more complex radicals; r—MR,). - a radical -R2\ / in which Rx and have the meaning given above and m is an integer from 0 to 3, - a radical -Ra-A-R* in which R2 has the meaning given above, R* denotes a linear or branched alkyl radical containing from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms, or a (Rl)ni and A symbolises one of the radical <3 following groups: —0—, —CO-, -COO- , -N-, -CO—N—, -N»NRs Rs -S-, -S02-.

In these formulae, R5 denotes a hydrogen atom or a linear or branched alkyl radical containing from 1 to 4 carbon atoms, preferably a methyl or ethyl radical. - 7 10 When n is greater than 1 the radicals R may be identical or different and 2 successive carbon atoms of the benzene ring may be joined together by a ketal bridge, such as methylenedioxy or ethylenedioxy radicals external to the ring. n is preferably equal to (0)-1-2 or 3.

Among all the abovementioned radicals Q, those very preferably used in the process of the invention are the trihalomethylcarbinols corresponding to the general formula (I) in which Q denotes an aryl radical corresponding to the general formula (II) in which: - n is equal to 0, 1, 2 or 3, - R denotes one of the following functional groups: - a linear or branched alkyl radical containing from 1 to 4 carbon atoms, - a linear or branched alkoxy radical containing from 1 to 4 carbon atoms, - a methylene- or ethylenedioxy radical, - an -OH group, - a -CHO group, - a phenyl or benzyl radical, - a halogen atom.

By way of examples of trihalomethylcarbinols corresponding to the general formula (I) in which Q denotes an aryl radical of general formula (II) there may be mentioned: 2-hydroxy-l-phenyltrichloromethylcarbinol, 3-hydroxy-l-phenyltrichloromethylcarbinol, 2-hydroxy2-hydroxy2- hydroxy3- hydroxy2-methoxy4-hydroxy-l-phenyltrichloromethylcarbinol, 3- methyl-l-phenyltrichloromethylcarbinol, 4- methyl-l-phenyltrichloromethylcarbinol, - methyl- 1-phenyltrichloromethylcarbinol, 4-methyl-l-phenyltrichloromethylcarbinol, l-phenyltrichloromethylcarbinol, 3-methoxy-1-phenyltrichloromethylcarbinol, 4-methoxy-l-phenyltrichloromethylcarbinol, 5-methoxy-l-phenyltrichloromethylcarbinol, 3- hydroxy-4-methoxy-l-phenyltrichloromethylcarbinol, 4- hydroxy-3-methoxy-l-phenyltrichloromethylcarbinol, 3-hydroxy-4,5-dimethoxy-l-phenyltrichloromethylcarbinol, - 8 4—hydroxy-3,5—dimethoxy-1 -phenyl trichloromethylcarbinol, - hydroxy-1,3-phenylbis (trichloromethylcarbinol) , 2-hydroxy-3-amino-1-phenyltrichloromethylcarbinol, 2- hydroxy-4-amino-x-phenyl tr ichloroinethylcarbino 1, S 2 - hydroxy- 5-amino -1-phenyl trichloromethylcarbinol, 3- hydr oxy-2-amino-l-phenyl trichlorome thy lcarbinol, 2 -hydroxy-3-nitro- 1-phenyltrichloromethylcarbinol, 3- hydr oxy-4-nitro-l-phenyl trichlorome thy lcarbinol, 4- hydr oxy-3-nitro-1-phenyl trichloromethylcarbinol, 3-hydroxy-4-methyl-2-nitro-1-phenyltrichloromethylcarbinol, 2-hydroxy-3,5-diiodo-l-phenyltrichloromethylcarbinol , 2,3-dihydroxy-l-phenyltrichloromethylcarbinol, 2.4- dihydroxy-l-phenyltrichloromethylcarbinol, 2.5- dihydroxy-1-phenyltrichloromethylcarbinol, 2,6-dihydroxy-l-phenyltrichloromethylcarbinol, 3.4- dihydroxy-l-phenyltrichloromethylcarbinol, 3.5- dihydroxy-l-phenyltrichloromethylcarbinol, 3.5- dihydroxy-4-methyl-l-phenyltrichloromethylcarbinol, 2.3.4- trihydroxy-l-phenyltrichloromethylcarbinol, 2,4,6 -trihydroxy- 1-phenyltrichloromethy lcarbinol and 3.4.5- trihydroxy-l-phenyltriehloromethylcarbinol.

In the general formula (I) of the trihalomethylcarbinols, Q may denote a saturated carbocyclic radical or one containing 1 or 2 unsaturations in the ring, general containing from 3 to 7 carbon atoms, preferably carbon atoms, in the ring; it being possible for the said ring to be substituted by 1 to 5 radicals Rlf preferably 1 to 3, Rx having the meanings specified above for the substituents of the aryl radical of general formula (II).

As preferred examples of radicals Q there may be mentioned cyclohexyl or cyclohexenyl radicals optionally substituted by linear or branched alkyl radicals containing from 1 to 4 carbon atoms.

By way of examples of trihalomethylcar binds of formula (I) in which Q ie a cycloaliphatic radical there may be mentioned especially 1-(trichloromethylcarbinol)1-cyclohexene, 1- (trichloromethylcarbinol) cyclohexane, 1-methyl-2-(trichloromethylcarbinol)-1-cyclohexene, - 9 1-methyl-2-( trichloromethylcarbinol) eyelohexane, l-methyl-4-isopropyl-2-(trichloromethylcarbinol)1-cyclohexene and l-methyl-4-isopropyl-2-( trichloromethylcarbinol )cyclohexane.

As already mentioned, Q may denote a linear or branched, saturated or unsaturated acyclic aliphatic radical.

More precisely, Q denotes a linear or branched elkyl/ alkenyl, alkadienyl or alkynyl radical preferably containing from l to 12 carbon atoms.

The hydrocarbon chain may be optionally» - interrupted by one of the following groups: —0-, —CO—, —COO—, -N-, -CO-N-, -N-N-, t » -S-, -S02-. in these formulae, R« denotes hydrogen or a linear or branched alkyl radical containing from 1 to 4 carbon atoms, preferably a methyl or ethyl radical, - and/or bearing one of the following substituents: -OH, -COOH, -CHO, NO2, -CN, -NHz, -SH, -X, -CF3 The linear or branched, saturated or unsaturated acyclic aliphatic radical may optionally carry a ring substituent. A ring means a saturated, unsaturated or aromatic carbocyclic or heterocyclic ring.

The acyclic aliphatic radical may be joined to the ring by a valency bond or by one of the following groups: -0-, -CO-, -C00-, -N-, -CO-N-, -N=N-, ί ( Re R« -S—, -SOj-, R« in these formulae having the meaning given above.

As examples of ring substituents there may be envisaged aromatic or heterocyclic cycloaliphatic substituents, especially cycloaliphatic ones containing 6 carbon atoms in the ring, or benzenic ones, these ring substituents themselves optionally bearing 1, 2, 3, 4 or 5 identical or different radicals Rt, R3 having the — 10 — meaning given above.

By way of examples of trihalomethylcarbinols of formula (I) in which Q denotes an aliphatic radical there may be mentioned especiallyt 3-nitro-l,1,1-trichloro5 2-butanol, 1,1,1-trifluoro-2-pentanol, 3-nitro1.1.1- trichloro-2-pentanol, 4-methyl-l,1,1-trichloro2-pentanol, 1,1,1-trifluoro-2-hexanol, 3,3-dimethyl1.1.1- trifluoro-2-butanol, 2-hydroxy-4-methoxy1.1.1- trichloro-5-pentanol, 1,1,l-trichloro-2-heptanol, -hydroxy-4-methyl-6,6,6-trichloro-3-hexanone, 2-hydroxy1.1.1- trichloro-4-octanone, 2-hydroxy-6-methyl1, 1, l-trichloro-4 -heptanone, 4-ethyl-l,1,1-trichloro2-hexanol, 3-ethyl-l, 1, l-trichloro-2-heptanol, 2-hydroxy1.1.1- trichloro-4-nonanone, 2-hydroxy-7-methyl15 1,1,1-trichloro-4-octanone , 1,1,1-trichloro4,6,6-trimethyl-2-heptanol, 1,1,1-trichloro—2-nonanol, 2-hydroxy-1,1,l-trichloro-4-decanone, 2-hydroxy1.1.1- trichloro-4-undecanone, 1,1,1-trichloro2- dodecanol, l,l,l-trichloro-3-buten-2-ol, 1,1,l-trichloro-3-penten-2-ol, 3-methyl-l,1,1-trichloro3- buten-2-ol, 5,5,5-trichloro-l-penten-4-ol, 4-methyl1.1.1- trichloro-3-penten-2-ol, 4-methylene-i,1,1-trichloro-2-pentanol, 3-methyl-l,1,l-trichloro-3-penten2-ol, 4-methyl-1,1,1-trifluoro-3-penten-2-ol, 3,4-dimethyl-1,1,l-trichloro-3-penten-2-ol, 4-ethyl1.1.1- trichloro-3-hexen-2-ol, 1,1,l-trichloro-3-nonen2- ol, 1,1,l-4-tetrachloro-3-nonen-2-ol, 1,1,1-trichloro3- dodecen-2-ol, 7-bromo-1,1,l-trichloro-7-octen-3-yn2- ol, 8-bromo-l,l,l-trichloro-7-octen-3-yn-2-ol, 1,1,l-trichloro-3-nonyn-2-ol, 1,1,l-trichloro-3-decyn-2ol, 1,1,l-trichloro-4-(4-methyl-3-cyclohexen-i-yl)3- penten-2-ol, 9-trichloroethylollimonene, ( 3,4,5,6-tetrahydro)-4-nonatolyl-l,1,1-trichloro2-pentanol, 9-trichoroethylolparamenthane, 4-phenyl35 1,1,l-trichloro-3-penten-2-ol, 4-phenyl-l,1,1-trichloro2-pentanol, 4,6,6-trimethyl-l,1,l-trichloro-3-hepten2-ol, 4,6,6-trimethyl-l,1,l-trichloro-2-heptanol, -methyl-l , 1 , l-trichloro-5-hexen-2-ol, -methyl-l,1,l-trichloro-2-hexanol, 3,4-dimethylIE 913719 - 11 1,1,l-trichloro-2-pentanol and 4,6-dihydroxy-5-nitro2-(3,3,3-trichloro-2-hydroxypropyl)pyrimidine.

Q may also denote a monovalent heterocyclic radical, saturated or not, containing particularly 5 or 6 atoms in the ring, including 1 or 2 hetero atoms such as nitrogen, sulphur or oxygen atoms, it optionally being possible for the carbon atoms of the heterocyclic ring to be substituted, completely or in the case of only some of them, by radicals RT, Rx having the meaning given above for the substituents of the aryl radical of formula (II).

Q may also denote a polycyclic heterocyclic radical defined as being either a radical consisting of at least 2 heterocyclic rings, aromatic or not, containing at least one heteroatom in each ring and together forming ortho- or ortho- and pericondensed systems, or a radical consisting of at least one hydrocarbon ring, aromatic or not, and at least one heterocyclic ring, aromatic or not, together forming ortho- or ortho- and pericondensed systems.

By way of examples of trihalomethylcarbinols of formula (1) in which Q denotes a heterocyclic radical there may be mentioned 2-furyltrichloromethylcarbinol, 2-nitrofuryltrichloromethylcarbinol, 1-(5-methylfuryl)trichloromethylcarbinol, l-(N,N-diethyl-5-furamide)tri25 chloromethylcarbinol, 2-amino-4-hydroxy-6-methyl5-(trichloromethylcarbinol)pyrimidine, 4-hydroxyS-methyl-2-me thylamino-5-(2,2) ,2-trichloro-lhydroxyethyl)pyrimidine and 2-dimethylamino-4-hydroxy-6methyl-5-(2,2,2-trichloro-1-hydroxyethyl)pyrimidine.

Among all the trihalomethylcarbinols referred to above by way of illustration and without any limitation being implied, the process of the invention applies particularly well to the following compounds: - 4-methoxyphenyltrichloromethylcarbinol - 3,4-dimethoxyphenyltrichloromethylcarbinol - 2,5-dimethoxyphenyltrichloromethylcarbinol - 3-methoxy-4-hydroxyphenyltrichloromethylcarbinol - 5-methoxy-2-hydroxyphenyltrichloromethylIE 913719 - 12 carbinol - 4-hydroxyphenyltrichloromethylcarbinol - 2,5-dihydroxyphenyltrichloromethylcarbino1 - 3,4-dihydroxyphenyltrichloromethylcarbinol - 3,4-methylenedioxyphenyltrichloromethylcarbinol - 4-tert-butylphenyltrichloromethylcarbinol - 4-isopropylphenyltrichloromethylcarbinol - 3,5-di-tert-butylphenyl trichloromethylcarbinol - 4-methyl-l,1,l-trichloro-3-penten-2-ol - 4-methyl-l,l,l-trichloro-4-penten-2-ol.

The trihalomethylcarbinol compounds capable of being subjected to scission into aldehydes according to the process of the invention are obtained by processes described In the literature. In particular, they may be prepared by one or other of the methods of preparation mentioned by J.H.T. Ledrut and G. Combes in Industrie chimique beige no.6 (1962) p. 635 to 652.

Among these various processes for obtaining trihalomethylcarbinols, some are more suited than others to the preparation of some classes of compounds of this type.

Thus, for example, the compounds containing a mobile hydrogen can react with chloral (or bromal) to give the corresponding trihalomethylcarbinol.

An acidic catalyst such as aluminium chloride can be employed for reacting aromatic hydrocarbons such as veratrole (or 1,2-dimethoxybenzene) with chloral. In the case of this type of preparation reference may be made, apart from the abovementioned paper, to the paper by R. Quelet in the Bulletin de la Society Chimique de France (1954), p. 932.

By starting with phenols, chloral may be reacted in the presence of anhydrous potassium carbonate [see M. Pauly, Berichte der Deutschen Geeellechaft 5_6. 979 (1923)].

In accordance with the process of the invention, the scission of the trihalomethylcarbinol to the corresponding aldehyde is performed in an organic solvent in the presence of a salt with basic properties. - 13 A salt with basic properties is therefore involved as a catalyst: in the process of the invention.

A first essential requirement which governs the choice of the said salt is that it must be insoluble in the reac5 tion mixture.

Another characteristic of this salt is that its anion should exhibit a pK, specified within the ranges specified above.

Salts of alkali metals, of alkaline-earth metals 10 and/or transition metals of group VIII of the Periodic Classification are particularly suitable for the application of the process of the invention.

Alkali metal salts mean, in the present text, lithium, sodium, potassium, rubidium and caesium salts.

Among all these salts, the use of caesium and potassium salts is preferred.

Alkaline-earth metal salts mean, in the presence text, beryllium, magnesium, calcium, strontium and barium salts, in most cases it is preferable to employ barium salts.

As far as the transition metal salts are concerned, use may be made of salts of divalent, trivalent and tetravalent metals and particular mention may be made of the salts of divalent metals such as manganese, cobalt, nickel, copper and zinc, salts of trivalent metals such as iron, chromium, aluminium, rare-earth metals, namely yttrium and the metallic elements which have an atomic number from 57 to 71 and scandium. Among the various salts mentioned above, those preferably chosen are lanthanum and zinc salt3. with regard to the form in which the abovementioned metallic element(s) is(are) present, the following forms may be mentioned more especially: carbonates, hydrogen carbonates, fluorides, phosphates, hydrogen phosphates, pyrophosphates, sulphates, hydrogen sulphates, sulphites, hydrogen sulphites, borates and hydrogen borates.

By way of preferred basic salts, caesium carbonate is chosen. - 14 The various salts may be used as such or in a supported form, for example on inorganic oxides such as alumina, silica, natural or synthetic clays, and the like.

The salts used are in anhydrous or hydrated form, the difference being of no consequence, but the hydrated form is preferred.

According to the process of the Invention, the scission of the trihalomethylcarbinol to the correspond10 ing aldehyde is performed in an organic solvent which is an aprotic organic solvent of low or medium polarity. It is chosen so that it has a dielectric constant, measured between 20*C and 25*C, higher than 0 and lower than 20, preferably between 5 and 15.

Any organic solvent which is liquid under the reaction conditions, corresponds to the abovementioned characteristics and dissolves trihalomethylcarbinol may be used according to the invention.

In order to determine whether an organic solvent is suitable in the application of the process of the invention, reference may be made to the tables in the work: Techniques of Chemistry, II - Organic solvents p. 536 et seq., 3rd edition (1970).

As examples of slightly or moderately polar aprotic solvent which are capable of being used in the process of the invention, there may be mentioned aliphatic or aromatic hydrocarbons, halogenated or not.

Aliphatic or aromatic hydrocarbons which may be mentioned are hexane, heptane, octane, nonane, decane or cyclohexane, toluene and xylene.

Halogenated aliphatic or aromatic hydrocarbons which may be mentioned are: perchlorinated hydrocarbons such as especially carbon tetraahloride, tetrachloroethylene, hexachloroethane, hexachloropropene and hexa35 chlorobutadiene, partially chlorinated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,l-trichloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane, trichloroethylene, l-chlorobutane, 1,2-dichlorobutane, monochlorobenzene, 1,2-dichloroIE 913719 - 15 benzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,4-trichlorobenzene or mixtures of different chlorobenzenes, bromoform, bromoethane or 1,2-dibromoethane, monobromobenzene or mixtures of monobromobenzene with one or more dibromobenzenes, and 1-bromonaphthalene.

Use may also be made of solvents such as phenols, like phenol, o-cresol, m-cresol or p-cresol, or aliphatic or aromatic nitriles like hexanenitrile, octanenitrile and benzonitrile.

Another class of solvents which are also suitable for the invention is aliphatic or aromatic ethers and, more particularly, ethylene glycol dimethyl ether (or 1,2-dimethoxyethane), diethylene glycol dimethyl ether (or 1,5-dimethoxy-3-oxapentane), 1,8-dimethoxy15 3,6-dioxaoctane, 1,11-dimethoxy-3,6,9-trioxaundecane, propyl ether, isopropyl ether, butyl ether, methyl tertbutyl ether, pentyl ether, isopentyl ether, phenyl ether, benzyl ether, dioxane, anisole, phenetole, p-dimethoxybenzene and veratrole.

Also suitable for being used in the process of the invention are solvents such as phosphoric esters like, for example, butyl phosphate, tributyl phosphate, and the like.

Among all the abovementioned solvents, that preferably chosen is 1,2-dichlorobenzene.

A mixture of solvents may also be employed.

In accordance with the process of the invention, the scission reaction of trihalomethylcarbinols to the corresponding aldehydes is performed in the presence of a catalyst, namely a salt with basic properties, in a slightly or moderately polar aprotic organic solvent, the various compounds being used in the proportions defined below.

The concentration of the trihalomethylcarbinol in the organic solvent is not critical and may vary within wide limits, for example from 0.1 to 10 mol/litre. However, a concentration chosen between 0.5 and 2 mol/litre is preferred.

As far as the quantity of catalyst used, - 16 expressed in relation to the trihalomethylcarbinol, is concerned, this i3 such that the weight ratio basic salt/ trihalomethylcarbinol varies from 0.01 to 1.0, preferably from 0.30 to 0.505 A preferred alternative form of the process of the invention consists in performing the scission reaction of the trihalocarbinols in the presence of a small quantity of water.

It has unexpectedly been found, in fact, that the 10 presence of a quantity of water, expressed as the ratio of the number of moles of catalyst to the number of moles of water of between 0.5 and 10.0, and preferably between 2.0 and 8.0, not only makes it possible to have a very good reaction selectivity but also a higher conversion. 15 Thus, the water may be introduced in any form whatever, for example by the catalyst when a salt in a hydrated form is involved, or externally, by adding the desired quantity of water.

The reaction temperature may be between 25’C and 20 200’C and preferably between 80*C and 170‘C.

The reaction may be conducted at atmospheric pressure or at reduced pressure which is preferably between 10 and 500 millibars.

It is preferred to conduct the reaction at 25 atmospheric pressure but under a controlled atmosphere of inert gases such as nitrogen or the rare gases, for example argon.

The reaction period can vary very widely. It depends, inter alia, on the nature of the trihalomethyl30 carbinol, on its conversion and on the reaction temperature. In most cases it is between 15 minutes and 10 hours, preferably between 30 minutes and 5 hours.

From a practical view point, the reaction is easily carried out by charging the catalyst, the organic solvent and the trihalomethylcarbinol into the apparatus and then raising the reaction mixture to the desired temperature with stirring, optionally at reduced pressure, for the period needed for the reaction to be completed.

The order in which the reactants are introduced - 17 is not critical but that shown above is preferred.

The trihalomethane formed is generally removed by continuous distillation as it is being formed.

At the end of the reaction the reaction mixture contains the aldehyde formed, small quantities of unreacted trihalomethylcarbinol, the catalyst and the reaction solvent.

The reaction mixture is in the form of a clear solution in which the catalyst is suspended. It is thus particularly easy to recover the catalyst by conventional liquid/solid separation techniques such as decanting, filtration, filtration with suction or centrifuging.

The aldehyde formed is in most cases recovered by distillation at atmospheric pressure or at reduced pressure (10 to 500 millibars) if the aldehyde is a heavy aldehyde of high boiling point (for example 150°C or above). Examples of implementation of the invention are given below. 20 The following examples are given by way of illustration, no limitation being implied.

In the examples the following abbreviations denote: Conversion * (number of moles of trihalomethylcarbinol 25 converted)/(number of moles of trihalomethylcarbinol introduced)% Yield - (number of moles of aldehyde formed)/(number of moles of trihalomethylcarbinol introduced)% Selectivity = (number of moles of aldehyde formed)/ (number of moles of trihalomethylcarbinol converted)% EXAMPLE 1 The following are charged into a 50-cm3 threenecked round bottom glass flask fitted with a magnetic stirrer, a distillation system, an inlet for inert gas (argon), a thermometer and a heating device using an oil bath: - 1 g (4 mmol) of 4-methoxy-l-phenyltrichlomethylcarbinol, of formula: och3 H—C—OH I cci3 - 6.5 g of 1,2-dichlorobenzene.

The reaction mixture is kept stirred under inert gas atmosphere and at room temperature (25*C) until the 4-roethoxy-l-phenyltrichloromethylcarbinol has dissolved completely. g (3 mmol) of caesium carbonate is then charged.

The mixture is heated for 4 hours to a bulk temperature of 90 “c.

The chloroform is distilled off as the reaction proceeds.

The mixture is then allowed to cool to 25°C and the catalyst is separated off by filtration on a no. 3 glass sinter.

The organic phase is analysed by higher performance liquid chromatography (HPLC). 4.00 mmol of 4-methoxybenzaldehyde (anisaldehyde) were obtained.

A 100% conversion of 4-methoxy-l-phenyltrichloromethylcarbinol and a 100% selectivity for anisaldehyde were determined.

EXAMPLES .2 to 8 Example 1 was repeated, the only difference being that the nature of the catalyst used is changed: - Example 2 : caesium fluoride CsF - Example 3 : caesium hydrogen carbonate CsHCO3 - 19 - Example 4 : caesium carbonate Cs2CO3 “ Example 5 s caesium hydrogen phosphate Cs2HPOA - Example 6 : potassium fluoride deposited on alumina KF/AL2O3 - Example 7 s potassium carbonate K2CO3 - Example 8 : potassium carbonate K2CO3 In Examples 7 and 8 the reaction mass is heated to 130°C for 4 hours and 18 hours respectively.

The results obtained are listed in Table I.

Table I / Example Ref. 1 ! Catalyst ) Kunfcec of amsl of catalyst ί ι Conversion * flaw X —- Selectivity X 2 1 e.e 100 100 100 3 1 CsBCO, t— - .-.--4 5.2 47 47 100 1 4 ! Ca2CO3 1.5 95 95 100 5 CS2HiO424 . ! 61 61 100 6 KF/AljOj 9.9 | 72 67 99 -,- «λ “i 7.3 ΐ 72 72 100 : 9 «2=03 7.3 100 100 100 , EXAMfkE_9 Example 1 is repeated, the only difference being that 1,2-dichlorobenzene is replaced with anhydrous anisole. .2 g of anhydrous anisole are used, dried beforehand by passing over a 0.3 nm molecular sieve marketed by Frolabo. mmol of anisaldehyde are determined using HPLC, that is a 100% yield.

Example 1 is repeated, but 100 mg (0.3 mmol) of caesium carbonate are charged, calcined beforehand for 1 hour at 200*C at 4xl0‘2 mm of mercury.

The 1,2-dichlorobenzene was also dried on a 35 0.3 nm molecular sieve. 1.48 mmol of anisaldehyde and 2.48 mmol of unconverted 4-methoxy-l-phenyltrichloromethylcarbinol were determined by HPLC, which corresponds to a 38% - 20 conversion and a 97% selectivity.

COMPARATIVE TEST a Example 1 is repeated, but no caesium carbonate is charged.

The reaction mixture is stirred and is heated to 90’C for 4 hours. in the absence of any salt with basic properties there is no reaction.

EXAMPLES 11 to 15 Example 10 is repeated, the only difference being that x cm3 of water, accurately measured, are charged into the reaction mixture so as to fix the ratio r which is defined as being the ratio of the number of moles of catalyst to the number of moles of water.

Table II Sxtopl· Ref. z c Convaftlen X Yield X Selectivity X11 1 5.3 01 00 08 12 2 3 02 60 07 20 13 3 1 as 38 loo 14 10 0.0 24 24 100 15 20 0.3 24 24 100 The beneficial effect of the presence of water on the conversion of 4-methoxy-l-phenyltrichloromethyl25 carbinol is observed.

EXAMPLE 16 The following are charged into a 50-cm3 threenecked round bottom glass flask fitted with a magnetic stirrer, a distillation system, an inlet for inert gas (argon), a thermometer and a heating device using an oil bath: - 0.80 g (3 mmol) of 4-hydroxy-l-phenyltrichloromethylcarbinol, of formula - 21 OH I H-C-OH CCI3 - 4.80 g (5 ml) of diethylene glycol dimethyl ether.

The reaction mixture is kept stirred under an inert gas atmosphere and at room temperature until the 4-hydroxy-1-phenyItrichloromethylcarbinol has dissolved. 1 g (6.6 mmol } of caesium fluoride is then charged. The mixture is heated for 4 hours to a bulk temperature of 100’C. The chloroform simultaneously produced is dis- tilled off as the reaction proceeds.

The mixture is allowed to cool and the catalyst is filtered off on a no. 3 glass sinter.

The organic phase is analysed by high performance liquid chromatography. 3.7 mmol of 4-hydroxybenzaldehyde were obtained. A 100% conversion of 4-hydroxy-1-phenyltrichloromethylcarbinol and a 56% selectivity for 4-hydroxybenzaldehyde were determined.

EXAMPLES 17 to 20 Example 1 is repeated, the only difference being that the nature of the catalyst used is modified: - Example 17 : caesium carbonate Cs2CO3 - Example 18 : caesium hydrogen carbonate CsHCO3 - Example 19 : caesium hydrogen phosphate CszHPOA - Example 20 : potassium fluoride deposited on alumina ΚΓ7α12Ο3 The results obtained are listed in Table III.

Table III Example Raf. j Catalyst nmol Conversion » Selectivity 2 J Held 1 Ϊ 1 17 I C.jC03 j 6.1 100 22 ' 22 18 i c»bcOj : 6.5 100 53 j 53 19 cajHPO,, ; 7.2 100 54 20 L . . KF/AljOj { 6.« 90 40 36 10 EXAMPLE 2i Example 16 was repeated, the only difference being that: - 4.9 g of tributyl phosphate are charged instead of 4.8 g of diethylene glycol dimethyl ether, - the heating period is only 30 minutes.

A 74% conversion of 4-hydroxy-1-phenyltrichloromethylcarbinol , a 54% selectivity for 4-hydroxybenzaldehyde and a 40% yield were determined.

EXAMPLE 22 The following are charged into a 30-cm* reactor as described in Example 16, but fed with a stream of nitrogen Instead of a stream of argon: - 1 g (5 mmol) of 4-methyl-l,1,1-trichloro4-penten-2-ol, - 13 g (10 mmol) of 1,2-dichlorobenzene, - 1 g (3 mmol)*of caesium carbonate CsCO3.

The mixture is heated until a temperature of 160’C is obtained, and this is maintained for 1 hour.

The chloroform byproduct of the reaction and 3-methyl-2-butene' are entrained with a nitrogen stream and are trapped at -40’C with a mixture of acetonitrile and solid carbon dioxide.

The mixture is then allowed to cool to approximately 25*C and the catalyst is separated off by filtration on a no. 4 glass sinter.

The organic phase is analysed by gas phase chromatography. 1.5 mmol of 3-methyl-2-butenal and 1.5 mmol of chloroform were obtained.

A 94% conversion of 4-methyl-l,1,l-trichloro4-penten-2-ol and a 32% selectivity for 3-methyl-2butenal were determined.

Claims (24)

1. Process for the preparation an aldehyde by scission of the corresponding α-trihalogenated secondary alcohol, characterised in that the reaction is performed 5 in a slightly or moderately polar aprotic solvent and in the presence of a catalyst which is a salt with basic properties and which is insoluble in the reaction mixture.

2. Process according to claim 1, characterised in 10 that the α-trihalogenated secondary alcohol corresponds to the general formula (I): Q-CH-CXj (I) OH in the said formula, Q denotes an optionally substituted, monovalent hydrocarbon radical containing from 1 to 40 carbon atoms and x symbolises a halogen atom, chlorine, fluorine, bromine or iodine and, preferably, chlorine.

3. Process according to either of claims 1 and 2, characterised in that the α-trihalogenated secondary alcohol corresponds to the general formula (I) in which Q denotes a monovalent hydrocarbon radical, substituted or not, which may be a linear or branched, saturated or unsaturated acyclic aliphatic radical, or a moncyclic or polycyclic, saturated, unsaturated or aromatic carboxycyclic or heterocyclic radical.

4. Process according to one of claims 1 to 3, characterised in that the α-trihalogenated secondary alcohol corresponds to the general formula (I) in which Q denotes an aryl radical corresponding to the general formula (II) in the said formula (II): - n is an integer from 0 to 5, preferably from 0 to 3, - R denotes R lr one of the following groups or functional groups: - a linear or branched alkyl radical containing from 1 to 6 carbon atoms, preferably from 1 to 4 carbon atoms, - a linear or branched alkenyl radical containing from 2 to 6 carbon atoms, preferably from 2 to 4 carbon atoms, - a linear or branched alkoxy radical containing from l to 6 carbon atoms, preferably from 1 to 4 carbon atoms, - a radical of formula -Rj-OH -R 2 -cooh -r 2 -cho -r 2 —no 2 -r 2 -cn -Rs-NH 2 -r 2 -sh -r 2 -x -R2-CF 3 in the said formulae R 2 denotes a valency bond or a saturated or unsaturated, linear or branched, divalent hydrocarbon radical containing from 1 to 4 carbon atoms, and X symbolises a halogen atom, especially a chlorine or bromine atom. - R denotes R 3 , one of the following more complex radicals: /7—7*. 1^1 )b - a radical -R 2 in which R x and R 2 have 30 the meaning given above and m is an integer from 0 to 3, - a radical -R^-A-R* in which R 2 has the meaning given above, R* denotes a linear or branched alkyl radical containing from 1 to 6 carbon atoms, 35 preferably from 1 to 4 carbon atoms, or a - 26 /} NJ* 1 radical // -At and A symbolises one of the following groups: -O-, -co-, -N-, < -CO-N- 5 I 1 R, —s—, —SO2” , -COO-, , _n=nin these formulae, R 5 denotes a hydrogen atom or a linear or branched alkyl radical containing from 1 to 4 carbon atoms. 10 5. Process according to claim 4, characterised in that the α-trihalogenated secondary alcohol corresponds to the general formula (I) in which Q denotes an aryl radical corresponding to the general formula (II) in which n is greater than 1 and the radicals R are identi15 cal or different and two successive carbon atoms of the benzene ring are joined together by a ketal bridge, preferably by a methylene or ethylene radical external to the ring. 6. Process according to either of claims 4 and 5, 20 characterised in that the α-trihalogenated secondary alcohol corresponds to the general formula (I) in which Q denotes an aryl radical corresponding to the general formula (II) in which: - n is equal to 0, I, 2 or 3, 25 - R denotes one of the following functional groups: - a linear or branched alkyl radical containing from 1 to 4 carbon atoms, - a linear or branched alkoxy radical contain30 ing from 1 to 4 carbon atoms, - a methylene- or ethylenedioxy radical, - an -OH group, - a -CHO group, - a phenyl or benzyl radical, 35 - a halogen atom. 7. Process according to one of claims 1 to 3, characterised in that the α-trihalogenated secondary alcohol corresponds to the general formula (I) in which Q denotes a saturated carbocyclic radical, or one containing 1 or 2 unsaturations in the ring, generally containing from 3 to 7 carbon atoms, preferably 6 carbon atoms in the ring; it being possible for the said ring to

5. Be substituted by 1 to 5 radicals R lz preferably I to 3, R x having the meanings specified above in claim 4.

6. 8. Process according to claim 7, characterised in that the β-trihalogenated secondary alcohol corresponds to the general formula (I) in which Q denotes a cyclo10 hexyl or cyclohexenyl radical optionally substituted by linear or branched alkyl radicals containing from 1 to 4 carbon atoms.

7. 9. Process according to one of claims 1 to 3, characterised in that the β-trihalogenated secondary 15 alcohol corresponds to the general formula (I) in which Q denotes a linear or branched alkyl, alkenyl, alkadienyl or alkynyl radical preferably containing from 1 to 12 carbon atoms; it being possible for the hydrocarbon chain to be optionally: 20 - interrupted by one of the following groups: -O-, -CO-, —COO—, -N-, -CO-N-, -N=N-, Re Re —S—, —S0 2 **, 25 in these formulae, Re denotes hydrogen or a linear or branched alkyl radical containing from l to 4 carbon atoms, preferably a methyl or ethyl radical, - and/or bearing one of the following substituents: -OH, -COOH, -CHO, N0 2 , -CN, -NH 2 , -SH, -X, -CF 3 . 30 10. Process according to claim 9, characterised in that the α-trihalogenated secondary alcohol corresponds to the general formula (I) in which Q denotes a linear or branched, saturated or unsaturated, acyclic aliphatic radical bearing a ring substituent, it being possible for 35 the said acyclic aliphatic radical to be joined to the ring by a valency bond or by one of the following groups: -0-, -co-, -coo-, -N-, -CO-N-, -Ν*=Ν-, Re ~S—, —SOj—, 5 in these groups having the meaning given above in claim 9. · Process according to claim 10, characterised in that the α-trihalogenated secondary alcohol corresponds to the general formula (I) in which Q denotes a linear or

8. 10 branched, saturated or unsaturated, acyclic aliphatic radical bearing a cycloaliphatic, aromatic or heterocyclic substituent optionally bearing from 1 to 5 identical or different radicals Rj, as defined in claim 4.

9. 12. Process according to one of claims 1 to 3, 15 characterised in that the β-trihalogenated secondary alcohol corresponds to the general formula (I) in which Q denotes a monovalent heterocyclic radical, saturated or not, containing particularly 5 or 6 atoms in the ring, including 1 or 2 heteroatoms such as nitrogen, sulphur 20 or oxygen atoms, it optionally being possible for the carbon atoms of the heterocyclic ring to be substituted, completely or in the case of only some of them, by radicals R 1# Rj having the meaning given above in claim 4.

10. 13. Process according to one of claims 1 to 12, 25 characterised in that the β-trihalogenated secondary alcohol is: - 4-methoxyphenyltrichloromethylcarbinol - 3,4-dimethoxyphenyltrichloromethylcarbinol - 2,5-dimethoxyphenyltrichloromethylcarbinol 30 - 3-methoxy-4-hydroxyphenyltrichloromethylcarbinol - 5-methoxy-2-hydroxyphenyltrichloromethylcarbinol - 4-hydroxyphenyltrichloromethylcarbinol - 2,5-dihydroxyphenyltrichloromethylcarbinol - 3,4-dihydroxyphenyltrichloromethylcarbinol - 3,4 -methylenedioxyphenyltr ichloromethylcarbino 1 - 4-tert-butylphenyltrichloromethylcarbinol - 4-isopropylpheny1trichloromethylcarbinol - 29 - 3,5-di-teirt-butylphenyltrichloromethylcarbinol - 4-methyl-l,l,l-trichloro-3-penten-2-ol - 4-methyl-l,1,l-trichloro-4-penten-2-ol.

11. 14. Process according to one of claims 1 to 13, 5 characterised in that the catalyst is a salt whose anion has a pK^ in aqueous medium at 25*C of between 0 and 14, preferably between 0 and 11, and still more preferably between 0 and 8.

12. 15. Process according to one of claims 1 to 14, 10 characterised in that the catalyst is a salt of an alkali metal, of an alkaline-earth metal and/or of a transition metal of group VIII of the Periodic Classification.

13. 16. Process according to claim 15, characterised in that the catalyst is a lithium, sodium, potassium, 15 rubidium or caesium salt, preferably a caesium or potassium salt.

14. 17. Process according to claim 15, characterised in that the catalyst is a beryllium, magnesium, calcium, strontium or barium salt, preferably a barium salt. 20

15. 18. Process according to claim 15, characterised in that the catalyst is a divalent, trivalent or tetravalent metal salt of a transition metal of group VIII of the Periodic Classification.

16. 19. Process according to claim 15, characterised in 25 that the catalyst is a salt of a divalent metal such as manganese, cobalt, nickel, copper or zinc, a salt of a trivalent metal such as iron, chromium, aluminium, a rare-earth metal or scandium; the said salt is preferably a lanthanum or zinc salt. 30 20. Process according to one of claims 14 to 19, characterised in that the catalyst ie a metal salt in the following forms: carbonates, hydrogen carbonates, fluorides, phosphates, hydrogen phosphates, pyrophosphates, sulphates, hydrogen sulphates, sulphites, hydrogen 35 sulphites, borates and hydrogen borates. 21. Process according to one of claims 14 to 20, characterised in that the catalyst is caesium carbonate, caesium fluoride, potassium carbonate or potassium fluoride. - 30 22. Process according to one of claims 14 to 21, characterised in that the catalyst is a metal salt in anhydrous or hydrated form, used as such or in a supported form. 5 23. Process according to one of claims 14 to 22, characterised in that the ratio of the number of moles of basic salt to the number of moles of water is between 0.5 and 10.0 and preferably between 2.0 and 8.0. 24. Process according to one of claims 1 to 22, 10 characterised in that the organic solvent has a dielectric constant higher than 0 and lower than 20, preferably between 5 and 15. 25. Process according to claim 24, characterised in that the organic solvent is chosen from aliphatic or 15 aromatic hydrocarbons, halogenated or not, aliphatic or aromatic nitriles, phenols or aliphatic or aromatic ethers and phosphoric esters. 26. Process according to either of claims 24 and 25, characterised in that the organic solvent is chosen from

17. 20 the following solvents: hexane, heptane, octane, nonane, decane or cyclohexane, toluene, xylene, carbon tetrachloride, tetrachloroethylene, hexachloroethane, hexachloropropene and hexachlorobutadiene, dichloromethane, chloroform, 1,2-dichloroethane, 1,1,l-trichloroethane,

18. 25 1,1,2,2-tetrachloroethane, pentachloroethane, trichloroethylene, 1-chlorobutane, 1,2-dichlorobutane, monochlorobenzene, 1,2-dichlorobenzene, l,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,4-triohlorobenzene or mixtures of different chlorobenzenes, bromoform, bromoethane or 30 1,2-dibromoethane, monobromobenzene or mixtures of monobromobenzene with one or more dibromobenzenes, 1-bromonaphthalene, phenyl, o-cresol, m-cresol or p-cresol, hexanenitrile, octanenitrile, bezonitrile, ethylene glycol dimethyl ether (or 1,2-dimethoxyethane), 35 diethylene glycol dimethyl ether (or 1,5-dimethoxy3-oxapentane), 1,8-dimethoxy-3,6-dioxaoctane, 1,ll-dimethoxy-3,6,9-trioxaundecane, propyl ether, isopropyl ether, butyl ether, methyl tert-butyl ether, pentyl ether, ieopentyl ether, phenyl ether, benzyl - 31 ether, dioxane, anisole, phenetole, p-dimethoxybenzene, veratrole, butyl phosphate and tributyl phosphate.

19. 27. Process according to one of claims 24 to 26, characterised in that the organic solvent is 1,2-di5 chlorobenzene or anisole.

20. 28. Process according to one of claims 1 to 27, characterised in that the concentration of the β-trihalogenated secondary alcohol in the organic solvent varies between 0.1 and 10 mol/litre, preferably between 10 0.5 and 2 mol/litre.

21. 29. Process according to one of claims 1 to 26, characterised in that the weight ratio basic salt/e-trihalogenated secondary alcohol varies from 0.01 to 1.0, preferably from 0.03 to 0.50. 15

22. 30. Process according to one of claims 1 to 29, characterised in that the reaction temperature is between 25*C and 200*C, preferably between 80*C and 17O*C.

23. 31, a process according to claim 1 for the preparation of an aldehyde, substantially as hereinbefore described and exemplified.

24. 32. An aldehyde whenever prepared by a process claimed in a preceding claim.