Патент USA US3031516код для вставки
3,031,506 United States Patent ()??ce Patented Apr. 24,1962 1 one or two hetero atoms will be‘ present in any single bridge. If an amino nitrogen ‘atom is present in the 3,031,506 aforementioned bridges, its remaining valence ‘may be METHBD FGR THE PREPARATION 0F DIARYL KETQNES satis?ed by either a hydrogen atom or an alkyl group Reynold C. Fuson, Urhana, Ill., and Bruno M. Vittim berga, Philadelphia, Pa, assignors to Rohrn & Haas Company, Philadelphia, Pa, a corporation of Delaware of one to twenty-one carbon atoms, such as methyl, N0 Drawing, Filed July 29, 1958, Ser. No. 751,615 8 Claims. (ill. 260-591) carbon in nature, such as tetramethylene, hexamethylene, , ethyl, butyl, octyl, dodecyl, octadecyl, .and eicosyl. It will generally be preferable to have these bridges hydro octamethylene, dodecamethylene or tridecamethylene, and when one bridge is tetramethylene, the other may be _ This invention dealswith a method for the preparation 10 trimethylene, as indicated hereto-fore. The bridges may also contain alkyl substituents within the number of car bon atoms mentioned heretofore, such as 1,1,4,4-tetra of speci?c diaryl ketones. The present invention deals with a reaction between a speci?c aromatic compound and a speci?c 2,6-disub stituted benzoic acid in a manner to be more fully de scribed hereinafter. The 2,6~disubstituted beuzoic acid 15 reactants of this invention may bewrepresented by the _ formula I ' R3 R5 R1 ' 20 coon Ill-l R2 R1 and R2 indiivdually represent alkyl groups of one to three carbon atoms in which the three-carbon representa 25 tion is the iso structure and these may be methyl, ethyl, and isopropyl groups. R1 and R2 preferably represent the same alkyl group in any one compound but they may stand for different alkyl representations within the de?ni tion just given. R3, R4, and R5 may represent the same 30 or di?erent components and these individually include a hydrogen atom, an alkyl group of one to two carbon atoms, i.e. methyl or ethyl, an n-alkoxyl group of one to twenty-one carbon atoms, a phenoxyl group, or a phen oxyl group substituted with one to ?ve groups preferably ' 4-phenoxy-2,3,5,6-tetramethylbenzoic acid, 4-isopropyl-2,6-dimethylbenzoic acid, 4-tert-butyl-2,G-dimethylbenzoic acid, 4-( a,a-dimethyl) decyl-2,6-dimethylbenzoic acid, 2,6-dimethyl-3,4-rnethylenedioxybenzoic acid, 2,6-dimethyl-3,4-hexamethylenedioxybenzoic acid, 1,2,3,4,5,6,7,8-octahydroantbracene-9—carboxylic acid, 2,3—heXamethylene-5,6hexamethylenebenzoic acid, carboxylic acid, - 3 ,4,5,6,7 ,8-hexahydro-2 [ 1H] oxaanthracene-Sl-carboxylic acid, and R5 may be methoxyl, propoxyl, butoxyl, octoxyl, dec phenoxyl, m-nitrophenoxyl, p-methylphenoxyl, and the acid reactants include 2,6-dimethylbenzoic acid, 2-ethyl-6-methylbenzoic acid, 2,3,5,6-tetramethylbenzoic acid, 3-ethyl-2,5,6-trimethylbenzoic acid, 2,3,4,5,6-pentamethylbenzoic acid, 4-e-thyl-2,3,5,6-tetramethylbenzoic. acid, 4-bro-mo-2,3,5,6~tetramethylbenzoic acid, 4-methoXy-2,3,5,6-tetramethylbenzoic acid, 1,2,3,4,5,6,7,8-octahydro-2~azaanthracene-9-carboxylic acid, 1,2,3,4,5,6,7,8-octahydro-2-methyl-2—azaanthracene-9 ortho and para directing groups. Typically, in addition to the alkyl representations previously presented, R3, R4, , oxyl, 'dodecoxyl, tetradecoxyl, octadecoxyl, eicosoxyl, heneicosoxyl, phenoxyl, p-chlorophenoxyl, p-methoxy methyltetramethylene, l-methyltrimethylene, and the like. Typical representations of the 2,6-disubstituted benzoic 1,2,3,4,5,6,7,8-octahydro-2,7-diazaanthracene-9 40 like. In addition, when R3 and R4 represent hydrogen atoms, then R5 can also represent alkyl groups of three to twelve carbon atoms in any of the known structural con ?gurations but preferably branch chained, such as iso carboxylic acid, . 1,2,3,4,5,6,7,8-octahydro-2,7-dimethyl-2,7-diaza anthracene-Q-carboxylic acid, 1,2,3,4,5,6,7,8-octahydro-l-azaanthracene-IO carboxylic acid, 2,3,4,5,6,7,8-heptahydro-l-oxaanthracene-IO carboxylic acid, propyl, tert-butyl, hexyl, octyl, nonyl, tert-decyl, undecyl, 1,3,4,5,7,8,9,10-octahydro-naphth[2,3-c] [2,S]oxa and tert-dodecyl. Furthermore, it is possible for R3 and azepine-ll-carboxylic acid, ' R5 collectively or R4 and R5 collectively to represent a 2,3,4,5,6,7,8-heptahydro-l-thiaanthracene-IO bridge having the formula carboxylic acid, 50 in which n is an integer of one to ten, preferably one to two. In ‘addition, R1 and R3 collectively or R2 and R4 collectively, or both, may represent bridges contain ing from three to thirteen carbon atoms. When R1 and 55 R3, as well as R2 and R4, both represent bridges, then there is the requirement that the total number of carbon atoms in the two bridges must be at least seven. The term, bridges, in the above sense, is used to include both the carbon atoms in a direct chain and also these chains 60 with alkyl substituents vas will be apparent to one skilled 1,3,4,5,6,7,8-heptahydro-2-oxa-7-azaanthracene-9= carboxylic acid, 2,3,4,5,6,7,8-heptahydro-1-oxa-6-azaanthracene~l0 carboxylic acid, 5,6,7,8~tetrahydrobenz[f]isoindoline-9-carboxylic acid, 1,3,5,6,7,8-hexahydrobenz[f]isothianaphthene-9. carboxylic acid, 1 - 2,7r-dimethylal,2,3,4,5,6,7,8-octahydroanthracene-9 carboxylic acid, and Z-methyl-1,2,3,4,5,6,7,8-octahydroanthracene-9 carboxylic acid. in ‘the art. While is is preferable and usual that these The other reactant employed in the present process, the ' bridges be entirely hydrocarbon in nature, it is quite per speci?c aromatic compound, may be represented by the missible that they contain hetero atoms, such as oxygen, sulfur, and nitrogen. These hetero atoms will be present 65 in ether, thioether, amino, or substituted amino groups with the restriction that these hetero atoms must not be in the ortho position with respect to the carboxyl group and also that there be at least two carbon atoms between each of the hetero atoms present. There may be present 70 as many hetero atoms in these bridges as is possible with formula ‘in the above de?nition and restriction, but generally only II The symbols W, X, Y, and Z may represent hydrogen 3,031,506 3 4 atoms or alkyl groups of one to three carbon atoms, in It is important to note here that aluminum chloride should be employed at the milder temperatures within which the three-carbon atom member is iso in structure, in any possible combination of hydrogen atoms and de ?ned alkyl groups. If only two, or three of these sym the de?ned range or otherwise it sometimes causes un desired isomerizations. The preferred catalyst is phos bols represent hydrogen atoms,'then the remaining two UK phorous pentoxide, phosphoric acid and combinations or one may represent alkyl groups of up to twelve car thereof particularly those known as polyphosphoric acid bon atoms including all of the known con?gurations, in that higher yields and shorter reaction times are con sistently observed with this catalyst. The above agents such as normal, iso, and tertiary. It is also possible to have one or two chlorine or bromine atoms present may be de?ned in the present circumstances as carboxyl provided they are the only substituents. It is further 10 removing catalysts. A solvent of the volatile, but relatively high boiling, possible to have one or two n-alkoxyl substituents in which the alkyl portion contains from one to twenty-one inert organic type, may be desirable in some instances, particularly if the catalyst and reactants are solids. How carbon atoms or one to two phenoxyl or phenoxyl groups ever, if the catalyst, such as polyphosphoric acid, is liquid ortho- and para-directing groups” 15 or at least one of the reactants is liquid, then the reac Typical representations of W, X, Y, and Z, according tion proceeds favorably without a solvent. It is fre quently possible, when the aromatic hydrocarbon react to the above de?nition, in addition to the methyl, ethyl and isopropyl vgroups referred to heretofore include butyl, ant of Formula II, referred to hereinbefore, is a liquid, pentyl, hexyl, nonyl, decyl, and dodecylin any of the to employ an extra amount of said reactant to function substituted with from one to ?ve groups, preferably known spatial con?gurations, methoxyl, ethoxyl, pro poxyl, heptoxyl, octoxyl, dodecoxyl, octadecoxyl, eicos as a solvent as well. When a solvent is deemed neces- , sary or desirable, there may be employed'saturated ali oxyl, phenoxyl, p-chlorophenoxyl, p-methoxyphenoxyl, phatic hydrocarbons, such as hexane, decahydronaphtha lene, and the like, or high molecular weight aliphatic others, such as dipentyl ether, dihexyl ether, and the m-nitrophenoxyl, p-methylphenoxyl, and the like. Typical representations of the aromatic reactant just de?ned include benzene, 1,2,3,4-tetramethylbenzene, m 25 like. These may be removed at the conclusion of the xylene, o-xylene, 1,2,3-trimethylbenzene, 1,3,4-trimethyl benzene, toluene, anisole, 1,2-dimethoxybenzene, octa~ decyl phenyl ether, 2,4-di-tert-butylbenzene, l-methyl-3 tert-dodecylbenzene, 1,2-dichlorobenzene, 1,3-dichloro benzene, 1-bromo-3-chlorobenzene, chlorobenzene, bro mobenzene, and diphenyl ether. reaction as desired by known methods such as by distilla tion under reduced pressure. At the conclusion of the reaction, the diaryl ketone product, which may be represented by the formula 30 W . The present reaction is conducted in the temperature range of about 25° to 235° C., preferably 50" to 200° C., with the restriction that a temperature must be em ployed in this range at which the carboxyl-bearing react W X V 35 ' X if Y O Z Y Z ant is freed of its carboxyl group. This temperature may be determined by the fact that the carboxyl-bearing may be isolated by known methods. The present proc reactant, once freed of its carboxyl group, is generally ess provides a direct method for the preparation of the isolable or removable from the reaction medium by de?ned ketones in an ef?cient, controllable, and con known methods and frequently may be recognized by its 40 venient way free from the use of corrosive, poisonous, volatility or sublimity. The reaction is conducted until and troublesome reactants and intermediates. The pres the carboxyl group is substantially completely removed ent invention also provides an essentially one-step proc from the carboxyl-bearing reactant at which time the ess for making compounds whose preparation by known reaction is consummated and highest yields are obtained. methods would require three or more steps. The ketone One skilled in the art will be able to determine readily , products have known utilities as insecticides and fungi the necessary temperature within the de?ned range from cides. the teachings of this invention. The present process may be more fully understood It is preferred to use an excess of the aromatic hydro from the following examples which are offered by way carbon reactant. It is necessary for the successful con of illustration and not by way of limitation. Parts by summation of the reaction to react two equivalents of the Weight are used throughout. aromatic hydrocarbon reactant with one of the carboxyl 50 containing reactants, and it is preferred to employ an EXAMPLE 1 excess of the aromatic hydrocarbon reactant beyond that Preparation of Di-p-Anz'syl Ketone necessary to combine with the carboxyl-containing react ant in order to induce maximum yields of the desired Into a 200 ml. three-necked, ground-glass ?ask, ?tted product. with a condenser, stirrer, and stopper, is poured 35 parts It is ‘possible to employ an equivalent of two different of warm polyphosphoric acid. To this is added 2 parts of aromatic hydrocarbon reactants with an equivalent of the coarsely ground duroic acid and 35 parts of anisole. The carboxyl-bearing reactant to form a mixture of three products, two symmetrical. and one unsymmetrical, as will be apparent to one skilled in the art. It is pre ferred to employ two equivalents of a single aromatic hydrocarbon reactant in order to minimize problems of separation of product. The reaction is generally con mixture is stirred rapidly while the temperature is raised, by means of a sand bath, to 80° C. over a period of one hour. The temperature is held at 80° C. for four hours. The system is opened, and the temperature raised to 160° C. Where it is maintained for seven hours. The hot reac tion mixture is then poured into 100 parts of distilled water, and the ?ask is rinsed with water. The water ducted at atmospheric pressures but reduced pressures may be employed, if desired, as would be apparent to 65 organic mixture is extracted four times with ether. This one skilled in the art in applying the teachings of this ether solution is washed three times with aqueous 5% invention. sodium bicarbonate, and twice with distilled water; it is The present reaction requires a narrowly de?ned cata then dried over anhydrous sodium sulfate. 7 lyst, including phosphorous pentoxide, at least essentially The ?ltered ether solution is concentrated under water 85% phosphoric acid, combinations of phosphorous pent 70 aspirator vacuum and dried under high vacuum for ?ve oxide and the de?ned phosphoric acid, particularly those combinations known as polyphosphoric acid, and Lewis acids such as zinc chloride, ferric chloride, mercuric chlo ride, stannic chloride, aluminum chloride, boron tri ?uoride,.and boron tri?uoride etherates and complexes. 75 minutes, giving orange crystals. One crystallization from ethanol yields 1.35 parts of organe-tinted plates, M.P. 140°—143° C. (Literature value for di-p-anisyl ketone, 143°-144° C.). The yield is 50% of the theoretical amount. By concentration of the mother liquor it is pos 3,031,506 . . . 5 yield is 55-60%. employed in Example 1. In a similar manner, employing m-xylene and duroic ’ In like manner, there is prepared a ketone product of acid there is produced 2,4,2',4’-tetramethylbenzophenone, this invention by reacting octadecyl phenyl ether with 2 ethyl-6-methylbenzoic acid, using stannic chloride as the catalyst. - 6 butylbenzophenone, is isolated in a manner similar to that sible to obtain an additional quantity of crystals; the total an orange-red oil having a value 111,26 1.5853. ' EXAMPLE 5 ‘ EXAMPLE 2 Preparation of 2,3,4,5,2',3',4’,5’-0ctamethylbenzophenone Preparation of 4,4'-Di-(p-Phenoxybenzoyl)Diphenyl Into a 200 ml. three-necked ?ask ?tted with a condene ' Ether ser, mechanical stirrer, and glass stopper is placed 35 parts of warm polyphosphoric acid. Then 3 parts of 2,6-di Into ‘a 200 ml. three-necked ?ask ?tted with a re?ux condenser, stirrer, and glass stopper is placed 35 parts of methyl-3,4-methylenedioxybenzoic acid is added, with 35 parts of 1,2,3,4-tetramethylbenzene. The mixture is warm polyphosphoric acid. To this is added 2 parts of coarsely ground 4-phenoxy-2,3,5,6-tetramethylbenzoic stirred and the temperature is raised to 80° C. over a pe acid and 10 parts of diphenyl ether. The mixture is 15 riod of one hour, by means of a sand bath, and held at stirred while the temperature is raised to 80° C. (by this level for four hours. The temperature is then raised means of a Sand bath) over a period of one hour. The to 160° C. where it is maintained for four hours longer. temperature is held there for four hours. Then the tem The excess 1,2,3,4-tetramethylbenzene is removed at this perature is raised to 160° C. and maintained at this point temperature under vacuum. The reaction mixture is treat for seven hours while the excess diphenyl ether is re 20 ed in the manner described in Example 1. The product, moved under vacuum. The hot reaction mixture is then 2,3,4,5,2’,3',4',5'-octarnethylbenzophenone, is puri?ed by poured into 100 parts of distilled water and the ?ask is recrystallization from ethanol. rinsed with water. The water-organic mixture is extracted There is similarly produced a ketone of this invention with ether. The ether solution is washed several times by reacting benzene with 2,6-dimethyl-3,4-hexamethyl with aqueous 5% sodium bicarbonate, twice with distilled 25 enedioxy-benzoic acid, using ferric chloride as the catalyst. water and then is dried over anhydrous sodium sulfate. EXAMPLE 6 The drying agent is removed by ?ltration and the sol vent by evaporation at reduced pressure at a temperature Preparation of 2,2'-Dimethyl-4,4'-Di-Tertd I of 35° C. The product, 4,4’-di-(p-phenoxybenzoyl)di phenyl ether, is puri?ed by chromatography on alumina. Dodecylbenzophenone In a similar way, there is produced a ketone product of this invention by reacting 4—methoxy-2,3,5,6-tetrameth ylbenzoic acid with diphenyl ether, using zinc chloride as the catalyst. EXAMPLE 3 ‘In a 200 m1. three-necked ?ask ?tted with a condenser, stirrer, and glass stopper is placed 40 parts of polyphos phoric acid, 2 parts of 1-methyl-3-tert-dodecylbenzene and 10 parts of 1,2,3,4,5,6,7,8-octahydro-2-azaanthra cene-9-carboxylic acid. The mixture is stirred rapidly 35 while the temperature is raised to 80° C. over the period Preparation of 4,4’-Dichlorobenz0phenone Polyphosphoric acid (35 parts) is placed in a three necked ?ask ?tted with a condenser, mechanical stirrer of one hour and held there for four hours. The tem perature is then raised to 160° C. where it is maintained for four hours. The hot reaction mixture is then treated as described in Example 1. The product, 2,2'-dimethyl and glass stopper. To this is added, with vigorous stirring, 40 4,4'-di-tert-dodecylbenzophenone, is puri?ed by recrystal 35 parts of chlorobenzene and 3 parts of 1,2,3,4,5,6,7,8 lization from chloroform-ethanol. octahydroanthracene-9-carboxylic acid. The temperature is increased to 160° C. within a period of two hours, using a sand bath to e?ect heating, and held at this temperature In an analogous way, there is produced a ketone of this invention by reacting 2,7-dimethyl-1,2,3,4,5,6,7,8 octahydroanthracene-9-carboxylic acid with 1,2,3-trimeth for one-half hour longer. The system is then opened and 45 ylbenzene, using boron tri?uoride etherate as the catalyst. ' the temperature raised to 170° C. within a period of one half hour and maintained at this temperature for four hours longer. The work-up of the reaction mixture is carried out in the same manner as in Example 1. The We claim: _1. A method for the preparation of a diaryl ketone having the formula W product, 4,4'-dichlorobenzophenone, is puri?ed by recrys~ 50 tallization from ethanol. W X X 'In an analogous manner, there is prepared a ketone of this invention by reacting 1,3,4,5,7,8,9,10-octahydro naph-[2,3-c][2,5]oxaazepine-1l-carboxylic acid with 1 t? Y .0 Y N Z Z ‘ —X bromo-3-chlorobenzene, using 85% phosphoric acid as 55 which comprises reacting substantially two equivalents the catalyst. of a compound having the formula EXAMPLE 4 Preparation of 2,4,2',4’-Tetra~Tert-Butylbenz0phenone Polyphosphoric acid (40 parts) is placed in a three 60 necked ?ask ?tted with re?ux condenser, mechanical I. stirrer, and glass stopper. To this is added 2 parts of Y 2,3,4,5,6,7,8 - heptahydro-l-thiaanthracene-10-carboxylic with one equivalent of a compound having the formula acid and 10 parts of 2,4-di-tert-butylbenzene. The stirrer R3 R1 is started and the temperature of the mixture is raised to 65 80° C. over a period of one hour and held there for four hours. The system is opened and the temperature raised to 160° C. where it is maintained for four hours longer. The hot reaction mixture is then poured into 100 parts of distilled water and the ?ask rinsed with water. The 70 water-organic mixture is extracted twice with ether and twice with chloroform. The extracts are combined, washed with aqueous 5% sodium bicarbonate and twice R5- COOH l R4 ' l R1 in the temperature range of about 25° to 2359 C. until the carboxylrbearing reactant is substantially free of its .carboxyl group in the presence of a carboxyl-removing asidis:v type catalyst from the group ‘consisting of phos hydrous sodium sulfate. The product, 2,4,2',4'-tetra-tert 75 phorous pentoxide, at least essentially 85 % phosphoric with distilled water. The solution is then dried over an 3,031,506 8 acid, polyphosphoric acid, zinc chloride, ferric chloride,v mercuric chloride, stannic chloride, aluminum chloride, 4. A method for the preparation'of a diaryl ketone having the formula boron tri?uoride, and boron tri?uoride etherates, in which W, X, Y, and Z are members from the class consisting ' W of hydrogen, methyl, ethyl, isopropyl, tert-alkyl groups x of four to twelve carbon atoms, chlorine, bromine, n‘ alkoxyl groups of one to twenty-one carbon atoms, Y phenoxyl, chlorophenoxyl, methoxyphenoxyl, nitrophen ‘W X it0 Y z z ' oxyl, and methylphenoxyl, such that said n-alkoxyl, phen which comprises reacting substantially two equivalents of oxyl, substituted phenoxyl, chlorine, and bromine repre 10 a compound having the formula sentations are possible only when two to three of said W, X, Y, and Z represent hydrogen, R1 and R2 individually represent members from the class consisting of methyl, ethyl, and isopropyl groups, R3, R4, and R5 individually represent members from the class consisting of a hydro 15 gen atom, an alkyl. group of one to two carbon atoms, an n-alkoxyl group of one to twenty-one carbon atoms, with one equivalent of a compound having the formula phenoxyl, chlorophenoxyl, methoxyphenoxyl, nitrophen R1 oxyl, and methylphenoxyl, When R3 and R4 represent hy drogen atoms R5 additionally represents an alkyl group 20 m©ooon of three to twelve carbon atoms, R3 and R5 when con sidered collectively represent an oxygenated bridge hav ing the formula in the temperature range of about 25° to 235° C. in the —O—-(CI-I2)n—O presence of polyphosphoric acid in which R1 and R2 are in which n is an integer of 1 to 10 and R4 and R5 when 25 alkyl groups of one to three carbon atoms, R5 is a tert considered collectively represent an oxygenated bridge having the ‘formula alkyl group of four to twelve carbon atoms, and W, X, Y, and Z represent alkyl groups of one to three carbon ' atoms. in which n is an integer of one to ten, and at least one of 30 R1 and R3 when considered collectively and R2 and R4 when considered collectively represent alkylene bridges 5. A method for the preparation of a diaryl ketone having the formula containing from three to thirteen carbon atoms provided that when R1 and R3, considered collectively, and R2 and R4, considered collectively, both represent said alkylene 35 0 bridges, the total number of carbon atoms in the two said alkylene bridges must be at least 7 and in which these bridges contain from zero to two atoms from the class which comprises reacting substantially two equivalents of consisting of ether oxygen, thioether sulfur, and amino nitrogen provided that there be at least two carbon atoms a compound having the formula between any two atoms of said oxygen, sulfur and nitrogen. 2. A process according to claim 1 in which the reaction temperature range is about 50° to 200° C. and in which the reaction is conducted in the presence of an inert 45 Y volatile organic solvent, and the catalyst is polyphos phoric acid. - with one equivalent of a compound having the formula ~ 3. A method for the preparation of a diaryl ketone having the formula W 50 W X 0 x ‘i Y COOH R: O Y z z 55 in the temperature range of about 25° to 235° C. in the presence of polyphosphoric acid in which R1 and R2 are which comprises reacting substantially two equivalents of alkyl groups of one to three carbon atoms, n is an integer a compound having the formula of one to ten, and W, X, Y, and Z represent alkyl groups of one to three carbon atoms. 60 z 6. A method for the preparation of a diaryl ketone having the formula x Y with one equivalent of a compound having the formula / 65 R1 R: which comprises reacting substantially two equivalents of 70 - a compound having the formula W in the temperature range of about 25° to 235° C. in the presence of polyphosphoric acid in which R1 and R2 are alkyl groups of one to three carbon atoms and W, X, Y, and Z represent alkyl groups of one to three carbon atoms. i 0 00011 Y X 75 3,031,506 R1‘ @0001; 10 8. A‘ method for the preparation of a diaryl ketone having the formula with one equivalent of a compound having the formula w w X X ‘ ‘t Y O Y in ‘the temperature range of about 25° to 235° C. in the z z presence of polyphosphoric acid in which R1 and R2 are 10 which comprises reacting substantially two equivalents of alkyl groups of one to three carbon atoms and W and X a compound having the formula represent alkyl groups of one to three carbon atoms. 7. A method for the preparation of a diaryl ketone _ W having the formula W W X 15 z X X Y ‘If Y 0. Z with one equivalent of a compound having the formula Y Z R3 which comprises reacting substantially two equivalents of 20 R1 ' OOOH a compound having the formula W | Y with one equivalent of a compound having the formula R4 R2 in the temperature range of about 50° to 200° C. in the 25 presence of polyphosphoric acid in which R1 and R2 are alkyl groups of one to three carbon atoms, R3 and R4 are alkyl groups of one to two carbon atoms, and W, X, Y, and Z represent alkyl groups of one to three carbon 30 atoms. References Cited in the ?le of this patent UNITED STATES PATENTS (CHnn COOH 1,866,717 (C Hahn in the temperature range of about 50° to 200° C. in the presence of polyphosphoric acid in which n and m- are integers of tour to thirteen and W, X, Y, and Z repre sent alkyl groups of one to three carbon atoms. 35 Meyer et a1 ___________ __ July 12, 1932 OTHER REFERENCES Thomas: Anhyd. Aluminum Chloride in Org. Chem. pp. 683—4 (1941). Snyder et al.: I. Am. Chem. Soc, vol. 77, pp. 364-5 (1955).