Title of Invention

A PROCESS FOR THE PREPARATION OF COUMARIN

Abstract

This invention relates to a process for the preparation of coumarin, saligenol in the liquid phase is o.1xdized with molecular oxygen or a gas containing molecu1ar oxygen in an aqueous medium containing an alkali in the presence of a platinum based catalyst and a boron derivative and a bismuth derivative to produce salicylic aldehyde.This salicylic aldebyde is reacted with acetic anhydride In the presence of' sodium acetate to obtain coumarin. ABSTRACT 567/MAS/2001 This invention relates to a process for the preparation of coumarin. Saligenol in the liquid phase is oxidized with molecular oxygen or a gas containing molecular' oxygen in an aqueous medium containing an alkali in the presence of a platinum based catalyst and a boron derivative and a bismuth derivative to produce salicylic aldehyde. This salicylic aldehyde is reacted with acetic anliydride in the presence of sodium acetate to obtain coumarin.

Full Text

The present invention relates to a process for the preparation of coumarin. More particularly, the invention concerns the preparation of salicylic aldehyde froni ortho-hydroxybenzyl alcohol, usually known as saligenol. A number of processes for carrying out this oxidation have been developed. In particular, French patent FR-A-2 305 420 describes the oxidation of ortho-hydroxybenzyl alcohol in the liquid phase, using molecular oxygen or a gas containing molecular oxygen, in an aqueous medium containing an alkali, in the presence of a platinum or palladium based catalyst. The reaction is characterised in that oxidation is effected in the presence of a co-catalyst based on a bismuth derivative. The yields of platinum based derivatives, which produce better reaction yields than palladium based catalysts, are increased in accordance with that invention due to the presence of bismuth. Thus the published salicylic aldehyde yields are 77.6 % in the absence of bismuth, and 92.8 % in the presence of bismuth. An aim of the present invention is to provide a process which can further improve the oxidation reaction yield. We have now discovered a process for the preparation of a hydroxybenzaldehyde by oxidation of the corresponding hydroxybenzyl alcohol in the liquid phase, using molecular oxygen or a gas containing molecular oxygen, in an aqueous medium containing an alkali, in the presence of a platinum ■ based catalyst, characterised in that oxidation is carried our m the presence of a boron derivative and a bisrnuth derivative. We have discovered that, for a platinum based catalyst, the presence of a boron derivative together with the bismuth derivative results in yields of salicylic aldehyde on oxidation of saligenol which are even higher , and can reach 97 %. The presence of boron limits oxidation to the aldehyde stage, without forming the acid. The process of the invention can be applied to any hydroxybenzyl alcohol, i.e., to any aromatic compound with at least one -OH group and one -CHjOH group. The term "aromatic compound" means the conventional concept of aromaticity as defined in the literature, in particular by Jerry MARCH, Advanced Organic Chemistry, 3rd edition, John Wiley & Sons, 1985, p.37 ff. The invention is particularly suitable for the oxidation of hydroxybenzyl alcohols with the following formula (I): where radical -CHjOH is in the ortho, meta or para position with respect to the hydroxy group, the benzene nucleus may be substituted by one or more substituents R, which may be identical or different, and n is a number which is less than or equal to 3. In the following description of the present invention, the radical with formula is represented by the symbol "Ar". Any substituent can be present on the benzene nucleus provided that it does not interfere with the desired product. Examples of substituents R are, in particular, halogen atoms, preferably fluorine, chlorine or bromine, and alkyl or alkoxy radicals, preferably containing 1 to 12 carbon atoms, more preferably 1 to 4 carbon atoms. Examples of preferred hydroxybenzyl alcohols are: 2-hydroxybenzyl alcohol; - 2-hydroxy-4-methylbenzyl alcohol; 2-hydroxy-6-rae1:hylbenzyl alcohol; 2-hydroxy-6-ethoxybenzyl alcohol; 2-hydroxy-6-chloroben2yl alcohol. The process of the invention is of particular application to the industrial preparation of salicylic aldehyde by oxidation of saligenol. The boron derivatives are preferably selected from boric acids such as orthoboric acid, usually termed boric acid (or its precursor BjOj), metaboric acid, pyroboric acid and tetraboric acid. Metallic borates can also be used, in particular those of alkali or alkaline-earth metals; or of ammonium in their anhydrous or hydrated forms, in particular tertiary borates, hemiborates, monoborates, diborates, triborates, tetraborates or pentaborates, preferably of alkali metals, or of ammonium. A double salt containing boron can also be used, in particular metallic fluoborates, for example potassium fluoborate. Examples of suitable boron compounds are: sodium orthoborate; potassium orthoborate; sodium monohydrogen orthoborate; potassium monohydrogen orthoborate; sodium dihydrogen orthoborate; potassium dihydrogen orthoborate; orthoboric acid or its precursor, boric anhydride; sodium metaborate; tetrahydrated sodium metaborate; sodium tetraborate; decahydrated sodium tetraborate, or borax; pentahydrated sodium tetraborate; potassium metaborate; tetrahydrated potassium pentaborate; octahydrated potassium tetraborate; tetrahydrated ammonium pentaborate; tetrahydrated ammonium tetraborate. Boric acid or boric anhydride is preferably used. The quantity of boron derivative used is determined so that the ratio between the number of moles of boron derivative and the number of moles of hydroxybenzyl alcohol is between 0-1 and 3.0, preferably between 0.9 and 1.1. The co-catalyst is generally an inorganic or organic bismuth derivative in which the bismuth atom has an oxidation number greater than zero, for example 2, 3, 4 or 5. The residue associated with the bismuth is not critical if it satisfies this condition. The co-catalyst can be soluble or insoluble in the reaction medium. Examples of co-catalysts suitable for use in the process of the present invention are: bismuth oxides; bismuth hydroxides; salts of mineral hydrogen acids auch as; bismuth chloride, bromide, iodide, sulphide, selenide or telluride; salts of mineral oxyacids such as: bismuth sulphite, sulphate, nitrite, nitrate, phosphite, phosphate, pyrophosphate, carbonate, perchlorate, antimonate, arsenate, selenite or selenate; salts of oxyacids derived from transition metals, such as: bismuth vanadate, niobate, tantalate, chromate, molybdate, tungstate or permanganate. Other suitable compounds are salts of organic aliphatic or aromatic acids, such as: bismuth acetate, propionate, benzoate, salicylate, oxalate, tartrate, lactate or citrate; and phenates such as: bismuth gallate or pyrogallate. These salts and phenates may also be bismuthyl salts- Other inorganic or organic compounds are binary combinations of bismuth with elements such as phosphorus and arsenic; heteropolyacids containing bismuth and their salts; also aliphatic or aromatic bismuthines. Specific examples are: oxides: BIO; Bi2O2; Bi2O,; BijO5, hydroxides: Bi(OH)j, salts of mineral hydrogen acids: bismuth chloride BiClj; bismuth bromide BiBr,; bismuth iodide Bil,; bismuth sulphide BijSj; bismuth selenide BijSej; bismuth telluride salts of mineral oxyacids: basic bismuth sulphite Bi2(SO3)3,Bi2O,,5 H2O; neutral bismuth sulphate Bi2(S0«)j; bismuthyl sulphate (BiO)HSO4; bisrauthyl nitrite (BiO)NOj,0.5HjO; neutral bismuth nitrate BKNO3)3, 5HjO; the double nitrate of bismuth and magnesium 2Bi(N03)3,3Mg(N03)2,24H20; bismuthyl nitrate (BiO)N03; bismuth phosphite Bi2(P03H)3, 3HjO; neutral bismuth phosphate BiPO salts of oxyacids derived from transition metals: bismuth vanadate BiVO4; bismuth niobate BiNbO; bismuth tantalate BiTaO4; neutral bismuth chromate Bij(Cr04); bisrauthyl dichromate (BiO)2Cr207; acidic bismuthyl chromate H(BiO)Cr04; the double chromate of bismuthyl and potassium K(BiO)CrO1o; bismuth molybdate Bi2(Mo04)3; bismuth tungstate BijCWO4)3; the double molybdate of bismuth and sodium NaBi (MoO4) 2 basic bismuth permanganate Bi202(OH)MnO4, salts of organic aliphatic or aromatic acids: bismuth acetate BiC2H3O)3,; bismuthyl propionate (BiOC3H5O2; basic bismuth benzoate C6HsC02Bi(OH)2; bismuthyl salicylate C6H4CO2 (BiO > (OH); bismuth oxalate (020^)3812; bismuth tartrate BijC4H4OJ)3, 6H2O; bismuth lactate (C6H,05)OBi, THjO; bismuth citrate CjH507Bi, phenates: basic bismuth gallate C7H707Bi; basic bismuth pyrogallate C6H3(OH)2(OBi)(OH). Other suitable inorganic or organic compounds are: bismuth phosphide BiP; bismuth arsenide BijAs^; sodium bismuthate NaBi03; bismuth-thiocyanic acids H2[Bi(BNS)5] , HjCBKCNS)^] and 35their sodium and potassium salts; trimethylbismuthine Bi(0113)3, and triphenylbismuthine Bi(CjH5)3. Preferred bismuth derivatives for use in the process of the invention are: bismuth oxides; bismuth hydroxides; the bismuth or bismuthyl salts of mineral hydrogen acids; the bismuth or bismuthyl salts of mineral oxyacids; the bismuth or bismuthyl salts of organic aliphatic or aromatic acids; and bismuth or bismuthyl phenates- j A particularly suitable group of co-catalysts for use in the process of the invention is formed by: bismuth oxides BijOj and BijO4; bismuth hydroxide BliOH); neutral bismuth sulphate BijCSO)3,; bismuth chloride BiCl,; bismuth bromide BiBrj; bismuth iodide Bil3; neutral bismuth nitrate Bi(N0j)3,5HjO; bismuthyl nitrate BiO(N03); bismuthyl carbonate (BiO)jCO3,0-5H2O; bismuth acetate Bi(C2H302)3; bismuthyl salicylate C5H,C02(BiO)(OH). The quantity of co-catalyst used, expressed as the quantity of metallic bismuth contained in the co-catalyst with respect 5to the weight of platinum employed, can vary between wide limits. This quantity can be as low as 0.1 %, for example, and can also equal or exceed the amount of platinum employed without detriment. More particularly, the quantity is selected such that the concentration of metallic bismuth with respect to the hydroxybenzyl alcohol in the oxidation medium is 10 to 9 00 ppm by weight. The co-catalyst can be used in quantities in excess of about 900 to 1500 ppm, but there is no great additional advantage. ■> The platinum used jointly as the reaction catalyst can be of a variety of forms, for example: platinum black, platinum oxide, or the noble metal itself deposited on a variety of supports such as carbon black, calcium carbonate, activated aluminas and silicas, or equivalent materials. Catalytic masses based on carbon black are particularly suitable. The quantity of catalyst used, expressed as the weight of metallic platinum with respect to that of the alcohol to be oxidized, can be from 0.01 % to 4 %, preferably from 0.04 % to 2 %. The concentration of alcohol to be oxidized in the aqueous alkali solution is preferably such that precipitation is avoided and a homogeneous solution is retained. The concentration of alcohol in the aqueous solution is generally between 1 % and 60 % by weight, preferably between 2 % and 30 % by weight. In accordance with the process of the invention, oxidation is carried out in an aqueous medium containing an alkali in Ssolution. The alkali is generally sodium or potaesiiiin hydroxide. The proportion of inorganic base used is between 0.5 and 3 moles of inorganic base per mole of alcohol to be oxidized. One mode of carrying out the process consists in bringing )the aqueous solution containing the alcohol to be oxidized into contact with the molecular oxygen or gas containing molecular oxygen, the alkali , the platinum based catalyst. the CO-catalyst based on a bismuth derivative and the boron derivative, in the proportions indicated above. The operation lis carried out at atmospheric pressure, but can if necessary be carried out under pressure. The mixture is then stirred at the desired temperature until the necessary amount of oxygen required to transform the alcohol into the aldehyde has been consumed. The progress of the reaction is thus monitored by Omeasuring the quantity of oxygen absorbed. The reaction temperature used depends on the thermal stability of the prepared products. In general, the reaction is carried out in the temperature range of 10"C to 100'C, preferably 20'C to 60*C. 5 Following cooling if required, the catalytic mass is separated from the reaction mixture, for example by filtration, and the resulting liquid is acidified by addition of a protonic mineral acid, preferably sulphuric acid, to a pH Of less than or equal to 6. The desired hydroxybenzaldehyde )can then be isolated, for example by extraction using a suitable solvent (for example toluene) or by steam distillation, followed by purification using known procedures. In the process of the invention, in the case where hydroxybenzyl alcohol, more particularly saligenol, is prepared using the conventional techniques described in the literature, for example by condensation of phenol with formaldehyde in the presence of zinc acetate or calcium formate (United Kingdom patent GB-A-0 774 696), the boron derivative can be introduced during oxidation. In a further embodiment of the invention, the boron derivative is introduced during preparation of the hydroxybenzyl alcohol which is effected using a specific Sreaction sequence as particularly described in French patents FR-A-1 328 945 and FR-A-2 430 928. Thus, in a first step, a boric ester of phenol is prepared by reacting a phenol with boric acid (or boric anhydride), then the boric ester of the phenol obtained is reacted with )formaldehyde or a formaldehyde generator, for example trioxane. The boric esters obtained, termed "aryl borates" for simplicity, are complex mixtures of: phenol metaborates with formula (II): (Ar has the meaning given above). These mixtures may contain excess starting phenol. The proportion of each of these boric acid derivatives in the esterification mixture depends on the molar ratio of phenol/boric acid used. This ratio is generally between 0.8 and 3.0, preferably between 1.0 and 1.5. Thus, for a phenol/boric acid ratio of between 1-0 and 1.5, ithe mixture is mainly constituted by metaborates with formula (II); for ratios between 1.5 and 3.0, the mixture is mainly constituted by phenol pyroborates with formula (III) and acid borates with formula (V); for a ratio of 3.0 or close to 3.0, orthhoboratess with formula (IV) are practically the only components of the mixture- Aryl borates are prepared using known procedures, by reacting a phenol with boric acid. The phenol preferably has formula: Ar-OH (VI) where Ar has the meaning given above. Examples of phenols with formula (VI) are; phenol, cresols, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 3,4-xylenol, Omonomethylphenols, monoethylphenols, raonopropylphenols, monobutylphenols, monomethyl-, monoethyl-, monopropyl- and monobutylethers of pyrocatechol. hydroquinone or resorcinol, monochlorophenols, 2,3-dichlorophenol, 2,4-dichlorophenol, 2,5-dichlorophenol, 3,4-dichlorophenol, 3, 5-dichlorophenol, 52,4,5-trichlorophenol, 2,3,5-trichlorophenol, 2,3-dimethoxyphenol and 3,5-dimethoxyphenol. The preparation of an aryl borate by reacting a phenol with boric acid is carried out in a solvent which forms an azeotrope with the water from the esterification reaction. 3This latter is eliminated as it is formed by azeotropic distillation. Suitable solvents for the preparation of aryl borates are aromatic hydrocarbons such as benzene, toluene or xylene. Any other inert solvent which can allow azeotropic distillation of water may be used. Condensation is carried out in an anhydrous medium. The solvent used for preparing the aryl borate can be used. Under these conditions, the borate is not isolated from the medium after esterification but is reacted directly with the formaldehyde. The formaldehyde is preferably used in a quantity of 1 mole per mole of boric acid. It can deviate from this value without detriment and may be between 0.9 and 1.1. When a formaldehyde generator is used, the quantity of formaldehyde is calculated so that the quantity of formaldehyde available for reaction falls within the range defined above. The temperature at which the formaldehyde or its generator is condensed with the selected phenol is between 20OC and ,120'C, preferably between 40'C and lOO'C. A, hydroxybenzyl alcohol borate is produced. In a subsequent step, the hydroxybenzyl alcohol is liberated from the condensation medium using any known procedure, for example saponification, hydrolysis or alcoholysis. Saponification is the preferred procedure, consisting in treating the reaction medium with a base. The base is preferably an alkali metal hydroxide, more preferably sodium or potassium hydroxide. The quantity of base introduced depends on the nature of the aryl borate and is between 2.0 and 4.0 moles, preferably about 2.0 moles of alkaline base per mole of boric acid used. Following saponification, the complex alkaline salt of hydroxybenzyl alcohol and boric acid is in an aqueous solution iwhich can be used directly for oxidation carried out in the presence of platinum and bismuth, without the need to separate the constituents. Salicylic aldehyde can thus be prepared directly from phenol without isolating the intermediate products formed. Thus, the phenol is reacted with boric acid (or boric anhydride) to form a boric ester, which latter is then reacted with formaldehyde to produce a saligenine borate which, after saponification using an alkaline base, produces an aqueous solution of a complex alkaline salt of saligenol and boric tacid. This aqueous solution can thus be used directly for oxidation in the presence of a platinum based catalyst and a co-catalyst based on a bismuth derivative without the need to separate the constituents. Very high yields of salicylic aldehyde are obtained after loxidation using the process of the invention. The process of the invention is thus of particular interest for the preparation of salicylic aldehyde which can b« used, 0 inter alia, for the preparation of cumarxn. Salicylic aldehyde obtained using the process of the invention can be used as a starting material for the synthesis of cumarin: this is produced by a known cyclisation step which has been widely described in the literature. In particular, o the Perkin reaction for the preparation of cumarin can be cited, by reacting salicylic anhydride with acetic anhydride in the presence of sodium acetate (KIRK-OTHMER - Encyclopedia of Chemical Technology 7, p. 198. 3rd edition). Accordingly, the present invention provides a process for the preparation of coumarin comprising the steps of oxidizing saligenol in the liquid phase, using molecular oxygen or a gas containing molecular oxygen, in an aqueous medium containing an alkali, in the presence of (i) a platinum based catalyst and (ii) boron derivative and a bismuth derivative to produce salicylic aldehyde; and reacting said salicylic aldehyde with acetic anhydride, in the presence of sodium acetate to obtain the coumarin. The following examples illustrate the invention without Slimiting its scope. In the examples, the abbreviation Y (yield) means as follows: Y - number of molps of aldRhyde formed number of moles of saligenol used EXAMPLES 1 TO 4 The noble metal based catalyst used in the four examples was platinum in the form of a catalyst containing 2 % by weight of metal deposited on carbon black: the quantity used, expressed sas the weight of platinum with respect to that of the alcohol to be oxidized, was 0.036 %. The reactions of the examples were carried out in the presence or in the absence of boric acid. When using boric acid, the quantity used, expressed as the •weight of boric acid with respect to that of the alcohol to be oxidized, was 51 %. The reactions of the examples were carried out in the presence or in the absence of a bismuth based co-catalyst, in this case bismuth oxide: the quantity used, expressed as the weight of bismuth with respect to that of the alcohol to be oxidized, was 0.065 %. The procedure followed in each example was as follows: A 100 cm2 glass flask was provided with a central stirring system, a heating means, and a thermometer. It was connected to a pure oxygen supply to permit the volume of gas absorbed to be measured over time. The following was loaded into the reactor: EXAMPLE 1 * 8 cm2 of an aqueous 4N caustic soda solution (0.032 mole of caustic soda); 72 mg of platinum based catalyst (i.e., 1.44 mg of platinum); 4 g (0.0323 mole) of ortho-hydroxybenzyl alcohol and 34 cm^ of water. EXAMPLE 2 * Example 1 was repeated but 2.9 mg of bismuth oxida (2.6 rag 5of bismuth) was added. EXAMPLE 3 * Example 1 was repeated, but 8 can3 of an aqueous 4N (0.032 mole) caustic soda solution was added and the quantity of diluting water was reduced by 8 cm3 to retain the same alcohol .Oconcentration in the mixture to be oxidized. EXAMPLE 4 Example 3 was repeated but 2.9 mg of bismuth oxide (2.6 mg of bismuth) was added. After loading the reactants (Examples 1 to 4), the reactor 5was purged with oxygen and connected to the oxygen supply under a slight pressure corresponding to the weight of a 30 cm column of water. The reaction mixture was heated to a temperature of 45 "C and stirring was commenced (1000 rpm). 0 The mixture was stirred at the above temperature and the mixture was stirred at 45C until oxidation was complete (no more oxygen absorbed). The reaction results, i.e., the yields of salicylic aldehyde with respect to the alcohol to be oxidized, were determined by 51iquid chromatography, following acidification of the reaction mixture. The results obtained are shown in the table below. TABLE (I) EXAMPLE 5 The following were loaded into a 250 ml three-necked flask provided with a stirring apparatus, a heating sleeve and a column provided with a retrograder to reflux the solvent and >separate the water of reaction: 47 g of phenol (0.5 mole); 31 g of boric acid (0.5 mole); 15 g of toluene. The mixture was distilled for 3 hours and the carrier (toluene) was recycled to separate the theoretical quantity of water. Dilution with 75 g of toluene followed and 16 g of jtrioxymerhylene suspended in 25 g of toluene was added. The mixture was held at 80'C until the reaction with the formaldehyde was complete (about 3 hours). The solution of saligenine borate in toluene was hydrolysed at room temperature with a caustic soda solution prepared by ladding 200 g of water to 152 g of a 30 % by weight caustic soda solution. This was then decanted and the aqueous solution containing the sodium salts of saligenol and boric acid was separated out. This aqueous solution was oxidized directly using the procedure described in Example 4, except that it was not lecessary to add boric acid. Oxygen at atmospheric pressure was passed into the solution, to which the following had been added: 0.8 g of 2 % platinum black (16 mg of platinum); 0.035 g of bismuth oxide (31 mg of bismuth). ' until the volume of oxygen absorbed corresponded to the theoretical quantity required to transform the saligenol into salicylic aldehyde, namely about 1 hour. The catalyst was separated from the reaction mixture and the isalicylic aldehyde formed was liberated from its sodium salt by adding 200 ml of 5N sulphuric acid, then steam distilling or extracting using an appropriate solvent to isolate the salicylic aldehyde. 43 g of salicylic aldehyde was obtained, representing a yield of 68 % with respect to the phenol used. EXAMPLE 6* Example 5 was repeated but without the addition of bismuth 3xide to the aqueous solution containing the sodium salts of saligenol and boric acid (before oxidation). 23 g of salicylic aldehyde was obtained, i.e., a yield of 37 % with respect to the phenol used. EXAMPLE 7 The following were loaded into a three necked flask provided with a thermometer, a distillation column, a retrogradsr, a coolant and a separator: salicylic aldehyde (600 mmol) prepared in accordance with Example 5; acetic anhydride (1.90 mmol) in solution in acetic acid (3.47 g). This was refluxed and sodium acetate (2.1 mmol) was introduced in solution in acetic acid (3.47 g). The acetic acid was distilled by maintaining the reflux until the temperature at the column head was about 118 "C. After 2 hours 50 minutes of reaction, gas chromatographic determination of the cumarin showed a yield of 82 % of cumarin. A This application has been divided out of Indian patent appUcatioti no. l49/L4S/95, which relates to "A process for the preparation of a hydroxY benzaldehyde "'. Claim 1 of the above patent application reads as; "A process for the preparation of a hydroxybenzaldehyde such as herein described by oxidation of the corresponding hydroxybenzyl alcohol in the liquid phase, using molecular oxYgen or a gas containing molecular oxvgen, in an aqueous medium containing an alkali, in the presence of a platinum based catalyst, wherein oxidation is carried out in the presence of a boron derivative as described herein and a bismuth derivative as described herein". WE CLAIM: 1. A process for the preparation of coumarin comprising the steps of oxidizing saligenol in tlie liquid phase, using molecular oxygen or a gas containing molecular oxygen, in an aqueous medium containing an alkali, in the presence of (i) a platinum based catahst and (ii) boron derivative and a bismulh deri\ative to produce salicylic aldehyde; and reacting said salicylic aldehyde with acetic anhydride, in the presence of sodium acetate to obtain the coumarin. 2. The process according to claim 1, wherein the boron derivative is selected from boric acids, preferably orthoboric acid (or its precursor B2O3), metaboric acid, pyroboric acid and tetraboric acid; metallic borates, in particular those of alkali or alkaline-earth metals or of ammonium in their anliydrous or hydrated fonns, in particular metal tertiary borates, hemiborates, monoborates, diborates, triborates, tetraborates or pentaborates, preferably of alkali metals, or of ammonium; or double salts containing boron, in particular metallic fluoborates. 3. The process according to claim 2, wherein the boron derivative is orthoboric acid or boric anliydride. 4. The process according to claim 2 or 3, wherein the ratio between the number of moles of boron derivative and the number of moles of saligenol is between 0.1 and 3.0, preferably between 0.9 and 1.1. 5. The process according to and one of claims 1 to 4, wherein the bismuth-derivative is an organic or inorganic bismuth derivative selected from: bismuth oxides; bismuth hydroxides; bismuth or bismuthyl salts or mineral hydrogen acids, preferably a chloride, bromide, iodide, sulphide, selenide or telluride; bismuth or bismuthyl salts of mineral oxyacids, preferably a sulphite, sulphate, nitrite, nitrate, phosphite, phosphate, pyrophosphate, carbonate, perchlorate. antimonate, arsenate, selenite, or selenate; bismuth or bisinuthyl salts of organic aliphatic or aromatic acids, preferably an acetate, propionate, salicylate, benzoate, oxalate, tartrate, lactate or citrate; and bismuth or bismuthyl phenates, preferably the gallate or pyrogallate. 6. The process accoi'ding to claim 5, wherein the bismuth derivative is selected from: bismuth oxides Bi203 and Bi204; bismuth hydroxide Bi(OH)3; bismuth chloride BiCl3; bismuth bromide BiBrj; bismuth iodide Bilj; neutral bismuth sulphate Bi2(S04)3; neutral bismuth nitrate Bi(N03)3; 5H2O; neutral bismuthyl nitrate (BiO)N03; bismuthyl carbonate (BiO)2C03, O.SHjO; bismuth acetate Bi(C2H302)3; and bismuthyl salicylate C6H4C02(BiOXOH). 7. The process according to claim 5 or claim 6, wherein the quantity of the said bismuth derivative used is selected such that it provides in the medium; at least 0.\% by weiglit of metallic bismuth with respect to the weight of platinum used, and 10 to 900 ppm by weight of metallic bismuth with respect to the saligenol. 8. The process according to any one of claims 1 to 7, wherein the platinum catalyst is in the form of platinum black, platinum oxide, or tlie noble metal itself deposited on a support such as carbon black, calcium carbonate, activated aluminas and silicas, or equivalent materials, preferably carbon black. 9. The process according to claim 8, wherein the quantity of catalyst used, expressed as the weight of metallic platinum with respect to that of the alcohol to be oxidized, is 0.01 "o to 4 . preferably 0.04 to 2"o. 10. 'Hie process according to any one of claims 1 to 9, wherein oxidation is carried out in an aqueous medium containing 0.5 to 3 moles of sodium or potassium hydroxide per mole of the saligenol to be oxidized. 11. The process according to any one of claims 1 to 10, wherein o.xidation is carried out at a temperature of between 10°C and 100°C, preferably between 20°Cand60°C. 12. The process as defined by claim 1, wherein said saligenol is a complex salt of saligenol and said boron compound is boric acid. 13. The process as defined by claim 12. wherein said complex .salt of saligenol and boric acid is formed by reacting a phenol with boric acid or boric anh\dride and forming a boric ester, reacting said boric ester witli formaldehyde or a formaldehyde generator and forming a saligenol borate, and then saponi tying said saligenol borate into said complex salt of saligenol and boric acid. 14. The process as defined by claim 13, wherein the molar ratio phenol boric acid ranges from 0.8 to 3.0. 15. The process as defined by claim 14, said molar ratio ranging from 1.0 to 1,5. 16. A process for the preparation of coumarin substantially as herein described and exemplified.

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0567-mas-2001 abstract.pdf

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