CA2012779A1 - Process for the preparation of phosphino compounds - Google Patents

Abstract

Abstract Process for the preparation of phosphino compounds Phosphorus-containing compounds of the formula (I) (R1)(R2)P(O)-CR3R4-CHR5R6 (I) in which R1 and R2 are alkyl, alkoxy or optionally substituted phenyl, R3 and R5 are H, R, optionally substituted phenyl, ROCO-, RO-CO-RO-, halogen, CN, RO-, RO-RO-R-CO-, H2NCO-, RNHCO- or RRNCO-, in which R is alkyl, R4 and R6 have the same meaning as defined for R1 and R2 or are a divalent radical in which R7 is oxygen, NR* or sulfur, and R* is H, option-ally substituted phenyl or alkyl, are precursors for plant protection agents and fire retardants. According to the invention they can be prepared in high yields and high purity by reacting a compound (R1)(R2)P-OR8, in which R3 is alkyl or optionally substituted phenyl, with an alkene of the formula R3R4C=CR5R6 and at least an equimolar amount of aprotic organic substance such as alcohols, amines, phenols, thiophenols or anilines.

Description

2~1277~

HOECHS~ ARTIENGESE~LSCHAFT HOE 89/F 100 Dr. WE/PP

D~rip~ion Process for ~he preparation of phosphino compound~

The invention relates to a proce&s for the preparation o~
S phosphino compounds of the formula (I) R3 ~5 ~ _ C - H (I) in which Rl and R2 independently of one a~other are ~lkyl, alkoxy or optionally substituted phenyl, 10 R3 and R5 independently of one another are hydrogen, alkyl, unsubstituted phenyl or phenyl mono- or multisub titu~d by halogen or mono- or di~ub-stituted by alkoxy; or are alkoxycarbo~yl, alkoxycarbonylalkoxy, halogen, cyano, alkoxy, alkoxyalkoxy, alkylcarbonyl, ~lko~ycarbonyl-alkyl, carbamoyl, al~ylaminocarbonyl or dialkylaminocarbonyl, R4 and R6 independently of one ~nother are h~drogen, alkyl, un~ub~tituted phenyl or phe~yl mono- or multi.ubstituted by halogen or mono- or disub-~tituted by alkoxy; ~r are halo~en, alkoxy carbonyl, ~lkoxycarbonylalkoxy, cy~no, alkosy, alkoxyalXoxy, alkylcarbonyl, ~l~oxycarbo~yl-alkyl, caxbamoyl, al~ylaminocarbonyl or di-alkyl~minoc~rbonyl; or ~ointly sre a divalent radical of the formula -- CO -- ~ -- CO --, in which R7 i~ oxygenl a radical of the formula NR*, in which R* represent~ hydrogen, C~-C6-alkyl, ` :

20~277~

unsubs-ti-tuted phenyl or phenyl mono~ or mul-ti-substituted by halogen; or is sulfur, hich cor.prises reacting a compound of the formula (II) R1-p (II) in which R1 and R2 have the meanings defined above and R3 is alkyl or optionally substituted phenyl, toge-ther with a compound of the formula (III) C = C ~III) in which R3, R', R5, R6 and R7 have the meanings defined above, and with at least an equimolar amount of a protic organic substance except carboxylic acids.

The term 'alkyl' denotes, for example, a straight-chain, branched or cyclic alkyl such as methyl, ethyl, n- and i-propyl, n-, i-, t- and 2-butyl, pentyl isomers, hexyl isomers, cyclopentyl, cyclohexyl, heptyl and octyl-isomers. The term 'alkoxy' denotes an alkyloxy raclical comprising in the alkyl part the ~eanings cited above as examples of alkyl. The term 'optionally substituted phenyl' denotes an unsubstituted phenyl or a phenyl substituted, for example, by halogen, lower alkoxy or lower alkyl. The term 'halogen' denotes fluorine, chlor-ine, bromine ancl/or iodine, preferably chlorine.

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Of particular intere~t i~ a proc~ accordin~ to the invention, in which R1 and R2 independently of one another are Cl-Ct-alkyl, phenyl or Cl-C8-alko~y, preferably methyl, ethyl, phenyl, ~etho~y, ethoxy, propo~y or bu~oxy, in particular methyl, e~hyl, phenyl, methoxy or ethoxy, R3 and R 5 independently of one another are hydrogen, Cl-C~-al~yl, unsubst~tuted phenyl or phenyl mono- or multisub~tituted by halogen,o or ~re C2-C~-alkoxycarbonyl, ~2-co-a~cylcarbonyl, (Cl-C4-alkyl)~arbonyl-C1-C10 alkyl, halogen, c:y~no~ C1-CB-a1kOXY~ (C1-C4-a1kOXY)-C1~ a1kOXY~
carbamoyl, N-(Cl C~-alkyl3aminooarbonyl, N,N-di(Cl-C4-alkyl)aminocarbonyl, 1-(Cl-C~-alko~y)-l-hydroxymethyl or l,l-bis(C1-C~-alkoxy)~ethyl, R~ and R6 independently of one another ~re hydrogen, Cl-C~-alkyl, unsub~titut~d phenyl or phenyl mono- or multi~ubstituted by halogen; or are C2-C6-alkoxycarbonyl, C2-CB-alkylcarb~nyl~
( Cl-C4-alkyl ) carbonyl-Cl-C1O-alkyl, halogen, cyano, Cl-~6-alkoxy, ( Cl-C"~-alkoxy3 -Cl-C4-alkoxy, carbamoyl, N- ~ Cl-C4-alkyl ) aminocarbo~yl, N, N-di ( Cl-C4-alkyl ) aminocarbonyl; 1- ( Cl-C4-~lkoxy3 -l-hydroxymethyl or l,l-bis(C1-C4-alko~r)methyl;
or ~ointly are a divalent radical of the formula - CO - R7 - CO -, in which R7 i8 oxygen, a radical of the fo~mul~ NR*, ln whi~h R* represent~ hydrogen, tCl-C6)-alkyl, un~ub~tituted ph~nyl or phenyl mono- to tri~ub-3titllted by halogen or i8 ~ulfur.

The process acc:ording to the ~nvention, in which 35 Rl and R2 independently of one ano~her are methyl, ethylt methoxy, e~hoxy or phenyl, R3 is hydrogen, 2~127~

", R~ i~ hydrogen or (Cl-C~-alkoxy~carbonyl, Rs i~ hydrogen, R6 i~ hydrogen, halogen, cyano, (Cl-C4~alko~y)~ar-bo~yl or carbamoyl, preferably (C,-Ca-~lkoxy)-carbonyl or cyano is particularly preferred.

The compounds of the fon~ula (I),~re useful intermediate~
in the preparation o~ plant protection ~gents ( see for example EP-A-30,4~4, US-~-4,399,2B7) and fixe retardants (Angewand~e Nakromolekulare Chemie 105, pp. 203-215 (1982) and literature cited therein~. It i~ known that a few representa~ives of the compounds of the formula (I) are obtainable, for example, by reacting the compounds of the formula (II) with un~aturated fatty acid$ ~see Houben-Weyl, ~ethoden der org. Chemie, volume 12tl, pp. 259-260 (1963) and literature cited therein~. ~ow-ever, this proce~ gives yield~ of only 10 - 50 % which, becau~e of the high amounts of efflu~nt ga~e~ ~nd waste product~ formed, represents a serious drawback both technically and ecologically. The unreacted phosphorus component (I) must undergo a c08tly process of di~po6al, since these compounds repre~ent a fire and toxic hazard and have an ob~ectionable smell (~ee Houben-~eyl, Method-en der org. Chemie, Vol. 12~1, p. 14~. In addition, hecause of ~he po3r yield~, eo~tly purification oper~
ations are needed at the end of the reaction.

In compari60n with the k~own proces~e~, the pre~ent in~ention relate6 to a highly 6el~ctive, inexpensivs and ~imple pxoce~s which furn~hes the phosphino ~ompound~ of ~he formula (I~ in almo~t quantitative yields a~d in high puri~y.

The crude products obtained in an almost guantit~tive yield are usually B0 pure that they can be directly used for further ch~mical reactions.

For a number of rea~on6 the proce6~ according to the .

2~)~ 2779 invention i8 to be regarded as surprising. Thu~, for example, the reaction~ of the phosphorus ~mponents (II) with the alkenes (IlI) do not ~iV9 ri~e, according to examples in the literature, to t:he products (I) without reQorting to a protic organic ~ubstance. Only highly vi~cous polymeric produ~t~ are obtain~d ~ee Anionische Polymerisation, B. Vollmert, Grundrlss der Nakromoleku-laren Chemie, Springer-Verlag 1!962, p. 107 ff ~nd lS9, ~ee Compari~on ~xample I). The low yields of up to a maxLmum of 50 ~ in the examples d2scribed in the liter-ature are likewise due ~o competing polymerization reactions as ~econdary reaction~. The desired reac ions are in some ca~es ~o ~low that the polymerization becomes the main reaction. (Houben-Weyl, Methoden der org.
Chemie, vol. 12/1, pp. 259 - 260). Surpri~ingly, the addition according to the lnvention of protic organic 6ubstance~ succeeds in ~ubstantially suppres~ing the polymerization and in forming the 1s1 adducts of the formula (I) in almost qua~titative yields.

~he process according to the invention i~ ~urthermore to be regarded as surprising ina~much as it i8 precisely by the addition of protic organic substances to the reac-tions described in the literature in which phosphorus compounds of the formula (II) are react~d with unsaturat-ed fatty acids that yields of le~s than 30 ~ ~nd henceeven worse yield~ of the desired 1:1 addu~tE are obtained ~ee Compari~on ~xample II).

The preferred protic organic ~ubstance~ are alcohol~, in particular Cl-C6-alcohol~, for example, methanol, ethanol, propanol, i~opropanol, n~ , t- and 2-butanol, further polyhydric alcohol~ ~uch as ethanediol and glycerol, Cl-C6-mercaptan~, for example ~ethyl~ercaptan, e~hylmer captan, propylmercaptan and 1,2 ethanedithiol, amine~, in parti~ular mono- or di(Cl-C6-alkyl)amines, for e~ample methyl~mine, ethylamine, dLmethylamine and propylamine, phenols, thiophenol~, anilines and ~imilar compoundR.
Because the above sub~tances can be generally regarded as 20:L~7~9 ~'derivatives~' of water on account of their protic proper-ties, the process according to the invention cannot be carried out in the presence of water, in contrast -to the organic protic compounds described, since water rapidly hydrolyzes the phosphorus components of the formula (II) (Sander, Chem. Ber. 93 (1960) ].223). Since it is quite impossible to ob~ain products of the formula (I) with water as the protic substance because of hydrolytic reactions taking place (see also Comparison Example III), it was unexpected for the protic organic substances to be used according to the invention to be suitable for achieving high selectivity and yields.

The protic organic substances R-H employed in the process according to the invention in at least equimolar amounts serve as reactants and, if appropriate, as solvents, and are converted, depending on the course of the reaction, at least in part, for example, to ethers, thioethers, amines, phene-toles, thiophenetoles or substituted ani-lines of the formula R-R3, Ra having the meaning defined above. The products R-R8 are preferably removed from the reaction mixture during or at the end of the reaction, for example by distillation. ~xcess reactant or solvent R-H is preferably removed at the end of the reaction by vacuum distillation.

Carboxylic acids are likewise excluded from the process according to the invention. When in the process according to the invention organic acids, for example formic acid or acetic acid, are used as protic substances, virtually no products of the formula (I) are obtained (see Comparison Example IV). It follows that the protic organic substance must not possess too acidic character-istics. Whether a substance is suitable in the sense of the invention can be readily established in a preliminary experiment.

The procedure of the process according to the invention is for example such that the compounds of the 2~277~

formula (II) are dis~olved in the protic organic ~ub-stance and ~he alkenes (III~ are added ~o the reaction mix~ure at temperature~ be~ween -20C and 150C, prefer-ably be~ween 0 and 100C. I~ also poe~ible to add the components (II) and (III) to the protic orga~ic substance at the ~ame time.

It is equally pos~ible to sta~: with a ~i~ture of the alkene componen~ ( III) and the protic organic substance ~nd add the phosphorus comp~nent (II) to ~h~a ~olutio~.

The protic organic ~ubstances ~re u~ed i~ at least equimolar ~mount6. In amount~ greater than eguimolar they can be additionally employed in the sen~e of an or~anic solvent.

The proces~ may be carried out without solYent or with excess protic organic substance ~ 801vent and/or in the presence of ~u~tomary organic ~olvent~ whieh are inert under the reaction conditions. ~xample~ of the last-named ~olvents are 601vents ~uch as op~ionally halogena~ed, aliphatic, cycloaliphatic, aromatic or araliphatic hydrocarbons, aliphati~ or cycloaliphatic ether~, for example poly~lycol dialkyl ethers, as well as ketones and esters. It iB expedient to perform the proce~s in an inert gas ~tmosphers, for example under n~trog~n, in order to prevent oxygen inter~ering with the reaction.

The process according to ~he invention may be ~ontinuous or di~continuous.

The process according ~o the invention i5 elucidated in greater detail by the examples below.

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EXAMPLE 1:

Methyl 3-(methoxy-methylphos~hin~l)propionate 80 g of methanol are mixed at room temperature under nitrogen with 216 g of dimethyl me-thanephosphonate and the mixture is treated dropwise at room temperature with 172 g of methyl acrylate, the temperature rising to 70C.
A-t the end of the dropwise addition the mixture is further stirred for 1 hour, at the end of which period about 90 g of dimethyl ether have separated in a fitted cooling trap. Excess methanol used as solvent is then removed by vacuum distillation. The crude product is obtained in a yield of 365 g with a 96.4 % purity, which represents a theoretical yield of 97.7 %. The boiling point of a distilled sample is 96C at 0.027 mbar. The lH-NMR spectrum and the CHP analysis of the product correspond to those of a comparison sample, synthesized by an independent route.

EXAMPLE 2:

Ethyl 3-(methoxy-methylphosphinyl)propionate A flask filled with nitrogen and fitted with a cooling trap is charged with 216 g of dimethyl methanephosphon-ate; the contents are heated to 60C and a mixture of 200 g of ethyl acrylate and lO0 g of methanol is added dropwise in the course of 1 hour, the temperature rising to 65C. The reaction mixture is further stirred for l hour, during which period a total of 91 g of dimethyl ether are collected in the cooling trap. Excess methanol is removed by vacuum distillation. The crude product is obtained in a yield of 362 g with a 97.3 % purity, which corresponds to a theoretical yield of 97.9 %. The boiling point of a sample is 100 - 102C at 0.013 mbar.

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EXAMPLE 3:

Methyl 3-(methoxy-methYlPhosPhin~l)propiona-te A mixture of 86 g of methyl acrylate and 80 g of ethanol is added dropwise in the course of 30 minutes at 60C
under nitrogen to a solution o~ 108 g of dimethyl meth anephosphonate. The reaction mixture is then stirred at 60C for one hour. A total of 55 g of methyl ethyl ether are collected in the cooling trap. Excess e-thanol is -then removed by vacuum distillation. The crude product is obtained in a yield of 184 g with a 95.4 ~ purity, which corresponds to a theoretical yield of 97.5 %.

EXAMPLE 4:

3-(Methoxy-ethylphospinyl)prooionamide 71 g of acrylamide and 120 g of n-propylamine are mixed at room temperature under nitrogen and the mixture is heated to 50C. 122 g of dimethyl ethanephosphonate are added dropwise to the reaction solution in the course of 30 minutes. The reaction mixture is then stirred for 5 hours at reflux temperature and the solven-t (low-boiling solvent such as excess propylamine ~ N-methyl-N-propyl-amine) is removed by vacuum distillation. The crude product is obtained in a yield of 175 g with a 94.4 %
purity, which corresponds to a theoretical yield of 92.3 %.

The lH-NMR spectrum and the CHP analysis of the product are in agreement with the corresponding da-ta of a com-parison sample, synthesized by an independent route.

EXAMPLE 5:

3-(Ethoxy-propylphosphinyl)propionitrile 53 g of acrylonitrile are added dropwise under nitrogen at a reaction temperature of 70C to a mixture of 160 g of die-thyl propanephosphonate in 100 g of n-propylmer-captan in -the course of 2 hours. Af-ter a further 3 hours the solvent (low-boilin~ solvent such as C3H7SC2H5 and excess C3H7SH) is removed by vacuum distillation; the crude product is obtained in a yield of 173 g with a 95.4 % purity, which corresponds to a theoretical yield of 94.4 %. The boiling point of the product is 117 -118C at 0.027 mbar.

EXAMPLE 6:

Ethyl 3-(ethoxycarbonyl)-3-(e-thoxy-ethylphosphin~l)-propionate 172 g of diethyl fumarate are slowly added at 65 - 70C
under nitrogen to a mixture of 140 g of diethyl ethane-phosphonate in 46 g of ethanol. After a fur-ther 3 hours the solvent (excess ethanol and diethyl ether) is removed by vacuum distillation; the crude product is obtained in a yield of 285 g with a 95.7 % purity, which corresponds to a theoretical yield of 90.9 ~.

The lH-NMR spectrum and the CHP analysis are in agreement with the corresponding data of a comparison sample, synthesized by an independent route.

EXAMPLE 7:

Methyl 3-(dimethoxyphosphinyl)propionate 86 g of methylacryla-te and 100 g of isobutanol are mixed under nitrogen at room temperature and heated to 80C, 124 g of trimethylphosphite are added dropwise to -the reaction solution in the course of 1 hour. The reaction mixture is stirred for 5 hours at reflux temperature and the solvent (remainder of isobutanol and isobutyl methyl ether) is removed by vacuum distillation. The crude product is obtained in a yield of 173 g with a 94.1 %

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purity, which corre~pond~ to a theoretical yield of 83.0 ~. The bo~ling point i~ 104 - 106C at 0.93 mbar.

E~AMPL~ 8:

3-(DLmethylphosphinyl)propionitrile 135 g of isobutyl dimethylpho~p]hinate ~re ~lo~ly added under nitrogen at 20C to a mixture of 53 g of ~rylo-nitrile and 32 g of me~hanol, the temperature rising sl~wly to about S0C. The rea~tion mixture is heated for about 3 hours and the ~olvent (remainder of methanol and i~obutyl methyl ether~ i8 remo~ed by diatillation. The crude product i8 obtained in a yield of 125 g with a 95.3 % purity, which corresponds to a theoretical yield of 30.9 %. The boiling point of a distilled sample 98 -100C at 0.013 mbar.

EXAMP~E 9:

Methyl 3-~dimethylphosphinyl)-3-metho~ycarbonyl) propionate 135 g of isobutyl dLmethylpho~phinate and 144 g of dLmethyl maleate are added under nitrogen simult~neously dropwise from two ~eparate dkoppin~ funnels at about 70DC
to a solution of 67 g of ethylene glycol. After a further hour the reaction mixturQ i8 di~tilled under reduced pre3~ure, i.e. volatile constituent~ Are ~arefully removed by vacuum distillat~on. The crude product i8 ob~ained in a yield of 215 g with a 95.2 ~ purity, which corresponds to a theoreti~al yield of 91.8 %.

~he lH-N~R 6pectrum and the CHP analy~is correspond to a compari on ~ample synthecized by an independent route.
The boiling point of the product i8 128 - 130C at 0.013 mbar.

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~012~79 EXAMPLE 10:

Methyl ~-(pnenyl-metnox~phosphlnyl)-2-chloroproplona~e 138 g of dimethyl phenylphosphonate are slowly added at 20C under nitrogen to a solution of 120.5 g of methyl 2-chloroacryla-te and 94 g of phenol. After a reaction time of 3 hours at 70C phenetole is removed by vacuum distil-lation. The residue represents 267 g of crude produc-t with a 93.0 ~ purity, which corresponds to a theoretical yield of 90.1 %.

The 1H-NMR spectrum and the CHP analysis of the product correspond to those of a comparison sample, synthesized by an independent route.

COMPARISON EXAMPLE I: (without protic organic substance) 86 g of methyl acrylate are added to 108 g of dimethyl methanephosphonate at 70C and the reaction mixture is heated at 70C for a further 4 hours. The reaction mixture is worked up by vacuum distillation, yielding 194 g of a highly viscous oil which according to the lH-NMR and 31P-NMR spectra does not contain the desired methyl 3-(dimethylphosphinyl)propionate. If the reaction mixture is worked up by distillation, no distillable product is obtained, which points to polymerization occurring in the experiment.

COMPARISON EXAMPLE II: in accordance with examples from the literature (Houben-Weyl, Methoden der org. Chemie, volume 12/1, pp. 259-260 and literature cited therein) 108 g of dimethyl methanephosphonate are added dropwise at 70C to a solution of 86 g of methacrylic acid and 32 g of methanol in the course of 30 minutes. After a reaction time of 3 hours the reaction mixture is worked up by vacuum distillation.

. ' ~ ' 2~27~9 59 g of 3-(dimethylpho~phinyl~-2~methylpropionic ~id axe obtained with a 91.1 % purity, which corresponds to a theoretical yield of 29.5 %.

COMPARISON ~XAMPhE IIIs (in the presence of water as protic sub~tance) 108 g of dLmethyl ~ethanephosphonate are added dro~ e at an lnitial t~mpera~ure of 25C ~o a ~ollltion o~ 86 of methylacrylate and 20 g of wa1:er i~ the course o~ 30 minutes. Th~ temperature ri~e~ to 65C during the addl-tion. The reac~ion mixture i~ then heated ~or 3 hours at 70C.

After working up of the reaction mixture by vacuum distillation, no methyl 3-(dimethylphosphinyl)propionate is ob~ained. On the other hand the hydroly~i~ product methyl methanephosphonate~ which could be i~ola~ed in an amount of 91 g by distillation, i~ obtained in a yield of 91.4 % with a 94.4 % purity. ~he boiling poin~ of the di6tilled ~ample is 55 58C at 10 - 15 torr. ~he ~ ~MR
~pectrum and the CHP analysi~ corre~pond to the compound obtained from a compari~on sample, ~ynthe~ized by an independent route.

COMPARISON ~AMPLE IY: (in the presence of formic ~cid as protic polar substance) 108 g of dLmethyl methsnephosphonat~ are ~dded dropwise at 70C to a solution o 86 g of ~ethylacryl~te and 50 g of formic acid ln the course of 2 hour~ And the reac~
mixture i~ heated ~t 70C ~or 2 hours. After ~orking up the xeaction mi~tur~ by vacuum distillation, 123 g of a crude produc~ are obtained ~hich fro~ it~ lH-~R and 31P-NMR spectra and gas chromatographic a~alysis cont~ins none of the desired product. The reaction mixture i~
composed of several ~ubstan es, the bulk of them ~eing acid compoundR of pho~phoru~ i~ the oxidation ~tage V.

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Claims (9)

1. A process for the preparation of compounds of the formula (I) (I) in which R1 and R2 independently of one another are alkyl, alkoxy, unsubstituted or substituted phenyl, R3 and R5 independently of one another are hydrogen, alkyl, unsuhstituted phenyl or phenyl mono- or multisubstituted by halogen or mono- or disub-stituted by alkoxy; or are alkoxycarbonyl, alkoxycarbonylalkoxy, halogen, cyano, alkoxy, alkoxyalkoxy, alkylcarbonyl, alkoxycarbonyl-alkyl, carbamoyl, alkylaminocarbonyl or dialkylaminocarbonyl, R4 and R6 independently of one another are hydrogen, alkyl, unsubstituted phenyl or phenyl mono- or multisubstituted by halogen or mono- or disub-stituted by alkoxy; or are halogen, alkoxy-carbonyl, alkoxycarbonylalkoxy, cyano, alkoxy, alkoxyalkoxy, alkylcarbonyl, alkoxycarbonyl-alkyl, carbamoyl, alkylaminocarbonyl or di-alkylaminocarbonyl; or jointly are a divalent radical of the formula - CO - R7 - CO -, in which R7 is oxygen, a radical of the formula NR*, in which R* represents hydrogen, C1-C6-alkyl, unsubstituted phenyl or phenyl mono- or multi-substituted by halogen; or is sulfur, which comprises reacting a compound of the formula (II) (II) in which R1 and R2 have the meanings defined above and R8 is alkyl or optionally substituted phenyl, together with a compound of the formula (III) (III) in which R3, R4, R5, R6 and R7 have the meanings defined above, and with at least an equimolar amount of a protic organic substance except carboxylic acids.

2. The process as claimed in claim 1, wherein R1 and R2 independently of one another are C1-C8-alkyl, phenyl or C1-C8-alkoxy, R3 and R5 independently of one another are hydrogen, C1-C6-alkyl, unsubstituted phenyl or phenyl mono- or multisubstituted by halogen; or are C2-C6-alkoxycarbonyl, C2-C5-alkylcarbonyl, (C1-C4-alkyl)carbonyl-C1-C10-alkyl, halogen, cyano, C1-C6-alkoxy, (C1-C4-alkoxy)-C1-C4-alkoxy, carbamoyl, N-(C1-C4-alkyl)aminocarbonyl, N,N-di(C1-C4-alkyl)aminocarbonyl, 1-(Cl-CI,-alkoxy)-1-hydroxymethyl or 1,1-bis(C1-C4-alkoxy)methyl, R4 and R6 independently of one another are hydrogen, C1-C6-alkyl, unsubstituted phenyl or phenyl mono- or multisubstituted by halogen; or are C2-C6-alkoxycarbonyl, C2-C8-alkylcarbonyl, (C1-C4alkyl)carbonyl-C1-C10-alkyl, halogen, cyano, C1-C8-alkoxy, (C1-C4 alkoxy)-C1-C4-alkoxy, carbamoyl, N-(C1-C4-alkyl)aminocarbonyl, N,N-di(C1-C4-alkyl)aminocarbonyl, 1-(C1-C4-alkoxy)-1-hydroxymethyl or 1,1-bis(C1-C4-alkoxy)methyl;
or jointly are a divalent radical of the formula CO - R7 - CO -, in which R7 is oxygen, a radical of the formula NR*, in which R* represents hydrogen, (C1-C6-alkyl, unsubstituted phenyl or phenyl mono- to trisub-stituted by halogen; or is sulfur.

3. The process as claimed in claim 1 or 2, wherein R1 and R2 independently of one arlother are methyl, ethyl, methoxy, ethosy or phenyl, R3 is hydrogen, R4 is hydrogen or (C1-C4-alkoxy)carbonyl, R5 is hydrogen and R6 is hydrogen, halogen, cyano, (C1-C4-alkoxy) carbonyl or carbamoyl.

4. The process as claimed in one or more of claims 1 to 3, wherein alcohols, mercaptans, amines, phenols, thio-phenols or anilines or mixtures of these substances are used as protic organic substances.

5. The proces as claimed in one or more of claims 1 to 4, wherein the temperature for the reaction of the compounds (II) and (III) is between -20°C and 150°C.

6. The process as claimed in claim 5, wherein the temper-ature for the reaction of the the components (II) and (III) is between 0°C and 100°C.

7. The process as claimed in one or more of claims 1 to 6, wherein the process is carried out in the customary organic solvents or mixtures thereof.

8. The process as claimed in claim 7, wherein excess protic organic substance is used as organic solvent.

9. The process as claimed in one or more of claims 1 to 8, wherein the reaction is performed in an inert gas atmosphere.