Process for preparing 1,2-oxa-phospholanes

Preparation of 2,5-dioxo-1,2-oxa-phospholanes having general formula (I) ##STR1## wherein R.sup.1 represents an alkyl group being optionally substituted and having up to 18 carbon atoms, a cycloalkyl group having up to 8 carbon atoms, an alkenyl group having up to 8 carbon atoms, an aryl group having up to 14 carbon atoms being possibly substituted by lower alkyl groups, by alkoxy groups, by halogen or by lower alkyl radicals, by alkylated or dialkylated amino groups, or which represents an aralkyl group having up to 15 carbon atoms and being possibly substituted in the same way as the aryl group, PA0 Wherein R.sup.2 stands for a lower alkyl group or hydrogen and R.sup.3 stands for a lower alkyl radical, a phenyl radical being possibly substituted by halogen or lower alkyl groups, for a benzyl radical or for hydrogen.

It is a known fact that 2-chloroformylethyl-phosphinic acid chlorides which 
are easily accessible from alkyldichlorophosphines and 
.alpha.,.beta.-unsaturated carboxylic acids, may be cyclized with 
acetanhydride to yield 2,5-dioxo-1,2-oxa-phospholanes, acetylchloride 
being formed as by-product (V. K. Charjrullin, I. I. Sobcuk and A. N. 
Pudovik, Z. obsc. Chim. 37, 710 (1967), V. K. Chajrullin, R. M. 
Kondrat'eva and A. N. Pudovik, Z. obsc. Chim. 38, 288 (1968)): 
##STR2## 
Publications of the same authors have made known furthermore the 
cyclization of 2-chloroformethylethyl-phosphinic acid chlorides by means 
of 1 mole of ethanol or acetic acid to yield phospholanes. 
These processes have the disadvantage that 2-chloroformylethyl-phosphinic 
acid chlorides have to be prepared in a separate processing step, then 
purified by distillation and finally, in a second processing step, to be 
submitted to reaction with the cyclization agent to yield the 
corresponding phospholanes. 
It has now been found that 2,5-dioxo-1,2-oxa-phospholanes having general 
formula (I) 
##STR3## 
wherein R.sup.1 represents an alkyl group, optionally substituted, having 
up to 18 carbon atoms, preferably from 1 to 12, especially from 1 to 4 
carbon atoms, which may carry preferably as three, but especially one 
substituent halogen, especially chlorine, or a cycloalkyl group having up 
to 8 carbon atoms, especially cyclohexyl or cyclopentyl, an alkenyl group 
having up to 8 carbon atoms, especially vinyl or allyl, an aryl group 
having up to 14 carbon atoms, especially phenyl, which may be substituted 
-- preferably up to twice -- by low alkyl groups having up to 4 carbon 
atoms, lower alkoxy groups having up to 4 carbon atoms, halogen or by 
amino groups alkylated or dialkylated by lower alkyl radicals having up to 
4 carbon atoms, or which represents an aralkyl group being substituted in 
the same way as the aryl group, and having up to 15 carbon atoms, 
especially benzyl, wherein R.sup.2 stands for an alkyl group having up to 
4 carbon atoms, preferably methyl, or hydrogen and wherein R.sup.3 stands 
for an alkyl radical having up to 4 carbon atoms, especially methyl, a 
phenyl radical which may be substituted up to three times, preferably once 
or twice, by halogen, preferably chlorine, or low alkyl groups having up 
to 4 carbon atoms, preferably methyl, for a benzyl radical or for 
hydrogen, preferably at least one of the radicals R.sup.2, R.sup.3 
represents a hydrogen atom, may be obtained by reacting 
dihalogenophosphines of general formula (II) 
##STR4## 
wherein R.sup.1 has the same meaning as in formula (I) and wherein X 
stands for chlorine or bromine, preferably for chlorine, with an equimolar 
quantity of an .alpha.,.beta.-unsaturated acid of formula (III) 
##STR5## 
wherein R.sup.2 and R.sup.3 have the same meaning as in formula (I), and 
simultaneously, especially as a mixture, with an equivalent quantitiy of a 
compound having formula (IV) 
EQU r.sup.4 -- oh (iv) 
wherein R.sup.4 represents hydrogen or an acyl radical having from 2 to 12, 
preferably from 2 to 8, especially from 2 to 4 carbon atoms, being 
possibly substituted by a hydroxy group in .gamma.- or .delta.-position or 
being substituted from once to three times by halogen, especially by 
chlorine, or by a carboxyl group, or wherein R.sup.4 represents the 
radical --CO--COOH, an alkyl-sulfonyl radical, phenyl-sulfonyl radical, 
phenalkyl-sulfonyl radical or alkylphenyl-sulfonyl radical having up to 12 
carbon atoms, preferably up to 8 carbon atoms, or wherein R.sup.4 
represents a radical of formula (IVa) 
##STR6## 
wherein R.sup.5 represents an alkyl radical having up to 12 carbon atoms, 
preferably up to 8 carbon atoms, especially up to 4 carbon atoms, being 
possibly substituted from one to three times, especially once, by halogen, 
especially by chlorine, a cycloalkyl radical having up to 8 carbon atoms, 
especially cyclopentyl or cyclohexyl, an alkenyl radical having from 2 to 
12, preferably from 2 to 6 carbon atoms, especially vinyl or allyl and 
wherein R.sup.6 has the meaning as specified for R.sup.5 or is standing 
for a carboxylic acid group having from 2 to 4 carbon atoms or for 
HO(CH.sub.2).sub.3 -- or for HO(CH.sub.2).sub.4 --, or with an equivalent 
quantity of a compound having formula (V), 
##STR7## 
wherein R.sup.5 and R.sup.6 have the meaning as in formula (IVa) and 
wherein R.sup.7 has the meaning of R.sup.5 or represents a group of 
formula (IVa), or with an equivalent quantity of mixtures of compounds 
having formulae (IV) and (V) and by isolating the reaction products. 
By equivalent quantities, calculated on 1 mole of the starting components 
having formulae (II) or (III) are to be understood the quotients of 
molecular weight of the compounds having formulae (IV) or (V), n 
representing the number of functional groups in the molecule of the 
compounds having formulae (IV) or (V). Functional groups in respect to the 
present invention may be: carboxyl groups, sulfonic acid groups, 
phosphinic acid groups, phosphinic acid ester groups and phosphinic acid 
anhydride groups. 
The process according to the invention yields not only the desired 
2,5-dioxo-1,2-oxa-phospholanes depending on the nature of the initial 
materials of formulae (IV) or (V), but also the reaction product from 
these latter. Thus there are obtained, besides phospholanes, for example 
acyl halides, sulfonyl halides, and phosphinic acid halides, which may be 
isolated and obtained in their pure state. Moreover, in the case of 
compounds suitable for cyclization such as 3- or 4-hydroxy-alkane 
carboxylic acid lactones and in the case of 3- or 
4-hydroxy-alkylphosphonic acids or their esters phostones are formed which 
may also be separated and obtained in their pure state. By doubling the 
employed quantity of compounds having formulae (IV) or (V) it is possible 
in some cases, of course, to obtain still further products, i.e. in the 
case of succinic acid or glutaric acid their inner anhydrides, in the case 
of phosphinic acids or phosphinic acid esters the corresponding phosphinic 
acid anhydrides. 
The following reaction schemes as per the invention may explain more 
clearly the reactions of dihalogenophosphines with .alpha., 
.beta.-unsaturated carboxylic acids and compounds having formulae (IV) or 
(V): 
##STR8## 
Surprisingly, the dihalogenophosphines can be reacted with a mixture of a 
.alpha.,.beta.-unsaturated carboxylic acid and a compound of formula (IV) 
or (V) in a reaction without isolation of intermediate products to yield 
2,5-dioxo-1,2-oxa-phospholanes, though dihalogenophosphines also react in 
the absence of .alpha.,.beta.-unsaturated carboxylic acids, with compounds 
of formulae (IV) or (V) to form products which do not paticipate in any 
reaction with .alpha.,.beta.-unsaturated carboxylic acids under the 
reaction conditions of the process according to the invention. Thus, 
carboxylic acids such a acetic acid, propionic acid and butyric acid 
react, even at a temperature below room temperature with alkyl 
dichlorophosphine to yield 1-hydroxy-alkane-1,1-bis-alkyl-phosphinic acids 
(German Offenlegungsschrift 2.153.998), which do not cyclize with 
.alpha.,.beta.-unsaturated carboxylic acids to yield 
2,5-dioxo-1,2-oxa-phospholanes. 
The reactions according to the invention as illustrated by the above 
equations 1 to 5 may be performed, of course, in two processing steps as 
well, namely first the addition of .alpha.,.beta.-unsaturated carboxylic 
acid and subsequently the cyclization in the same reaction vessel. 
It is to be considered a special advantage of the process according to the 
invention, that the so-called "one-vessel-reaction" (= reaction without 
isolation of intermediate products) does away with cumbersome processing 
steps such as isolation and purification of an intermediate product so 
that the overall reaction period may be cut down substantially. Moreover, 
the above-mentioned halides anhydrides and derivatives of phosphinic acid 
can be prepared by choosing a suitable compound of formulae (IV) or (V) 
and using a stoichiometric ratio of these compounds to the molar number of 
the two other reactants. 
Suitable dihalogenophosphines of the formula (II) that may be prepared 
according to known methods and utilized according to the invention are, 
for example: 
Methyldichloro-phosphine, ethyldichloro-phosphine, 
propyldichloro-phosphine, butyldichloro-phosphine, 
dodecyldichloro-phosphine, chloromethyldichloro-phosphine, 
vinyldichloro-phosphine, cyclohexyldichloro-phosphine, 
benzyldichloro-phosphine, phenyldichloro-phosphine, 
p-chlorophenyldichloro-phosphine and the corresponding dibromo-phosphines. 
Suitable .alpha.,.beta.-unsaturated carboxylic acids of formula (III) to be 
employed are for example acrylic acid, methacrylic acid, crotonic acid, 
1-ethyl-acrylic acid, 1-phenyl-acrylic acid. 
As suitable compounds of formulae (IV) or (V) may be considered for 
example: 
Acetic acid, propionic acid, butyric acid, caproic acid, monochloro-acetic 
acid, trifluoro-acetic acid, oxalic acid, malonic acid, succinic acid, 
glutaric acid, .gamma.-hydroxy-butyric acid, methane-sulfonic acid, 
ethane-sulfonic acid, propane-sulfonic acid, benzene-sulfonic acid, 
dimethyl-phosphinic acid, ethylmethyl-phosphinic acid, diethyl-phosphinic 
acid, methyl-propyl-phosphinic acid, methyl-propyl-phosphinic acid, 
methyl-dodecylphosphinic acid, diphenyl-phosphinic acid, 
dimethyl-phosphinic acid-ethyl ester, dimethyl-phosphinic 
acid-2-chloroethyl ester, methyl-ethyl-phosphinic acid isobutyl ester, 
methyl-hexyl-phosphinic acid-butyl ester, hydroxymethyl-methyl-phosphinic 
acid, 3-hydroxypropyl-methylphosphinic acid, dimethyl-phosphinic 
acid-anhydride, methyl-ethyl-phosphinic acid-anhydride, 
methyl-butyl-phosphinic acid-anhydride, methyl-phenyl-phosphinic 
acid-anhydride, diphenyl-phosphinic acid-anhydride. 
Preferred compounds are acetic acid, propionic acid, sulfonic acids, 
dimethyl-phosphinic acid, methyl-ethyl-phosphinic acid and 
methyl-ethyl-phosphinic acid-isobutyl ester. 
Generally, the process according to the invention is carried out in such a 
way that a mixture of an .alpha.,.beta.-unsaturated carboxylic acid and of 
a compound of formulae (IV) or (V) is added dropwise to the 
dihalogenophosphines. However, it is also possible to add the 
dihalogenophosphines to a mixture of the two other reactants. The 
dihalogenophosphines and the .alpha.,.beta.-unsaturated carboxylic acids 
are utilized in equimolar quantities, whilst the stoichiometric ratio of 
the compounds of formulae (IV) or (V) to the other reactants depends on 
whether e.g. halides or - especially in the case of bifunctional compounds 
- lactones, carboxylic acid-anhydrides or phosphinic acid-anhydrides are 
desirable by-products. Accordingly, the molar ratio of 
dihalogenophosphines or .alpha.,.beta.-unsaturated carboxylic acids to the 
monofunctional compounds of formulae (IV) and (V) may therefore be either 
1:1 or 1:2, whereas the bifunctional compounds of formulae (IV) and (V) 
may be employed at a molar ratio of 1:1 or 0.5:1 to the other reactants. 
As solubilizers or as diluents there may be added to the 
dihalogenophosphines or to the two other reactants inert solvents, for 
example aliphatic, cycloaliphatic, aromatic or araraliphatic hydrocarbons 
such as xylene, chlorobenzene, toluene, chlorotoluene, dichlorobenzene, 
benzene fractions boiling at a higher temperature, carbon chlorides such 
as methylene chloride, chloroform, 1,2-dichloroethane, 
1,2-dichloropropane, ethers such as tetrahydrofurane, dioxane, isopropyl 
ether, di-n-butyl ether, dimethoxy ethane, polyethylene-glycol-dialkyl 
ether and polypropylene glycol-dialkyl ether. However, it is preferable to 
carry out the process of the invention in the absence of inert solvents. 
The reaction temperature ought to be approximately from -20.degree. C. to 
+160.degree. C., preferably from 0.degree. C. to +100.degree. C., 
especially from +15.degree. C. to +80.degree. C. There is no need to keep 
the reaction temperature at a constant level by exterior cooling devices. 
When operating without a solvent it may be rather advantageous to allow 
the reaction temperature to climb to the melting point of the phospholane 
so as to reduce the viscosity of the reaction mixture. 
The reaction time varies generally from about 2 to 6 hours. The reaction 
mixture is subsequently stirred for approximately half an hour at a 
temperature of from 100.degree. to 130.degree. C. under normal pressure 
and furthermore stirred for half an hour at about 130.degree. to 
200.degree. C. under water jet vacuum. 
The 2,5-dioxo-1,2-oxa-phospholanes may generally be easily separated from 
the other reaction products by fractional distillation. Highly volatile 
reaction products can be eliminated while stirring the reaction mixture 
under normal pressure or under water jet vacuum. It is also possible, 
however, to separate and purify the reaction mixture by extraction with 
inert solvents or by recrystallization. 
The yields of 2,5-dioxo-1,2-oxa-phospholanes obtained represent about 
70-80% of the theoretical yield, calculated on the dihalogenophosphines of 
formula (II) employed. 2,5-dioxo-1,2-oxa-phospholanes are good 
flame-retardants which may be utilized for preparing barely flammable, 
linear polyesters. They represent furthermore valuable intermediate 
products which may be further processed e.g. to yield flameproofing agents 
.

The following Examples illustrate the invention: 
EXAMPLE 1 
2-methyl-2,5-dioxo-1,2-oxa-phospholane based on methyldichlorophosphine, 
acrylic acid and water 
A mixture of 225 g (3.12 mole) of acrylic acid and 56 g (3.12 mole) of 
water is added dropwise at 20.degree.-25.degree. C. to a solution of 365 g 
(3.12 mole) of methyldichlorophosphine in 600 ml of methylene chloride. 
During this operation a strong current of hydrogen chloride is discharged. 
The solvent is distilled off and the reaction mixture subsequently heated 
under water jet vacuum for about 4 hours to 130.degree.-150.degree. C. 
After distillation in a film evaporator (boiling point at 1 mm Hg: 
164.degree.-170.degree. C.) 322 g of 2-methyl-2,5-dioxo-1,2-oxa-phospolane 
are obtained, representing a yield of 77% of the theoretical yield, 
calculated on methyldichlorophosphine. 
EXAMPLE 2 
2-methyl-2,5-dioxo-1,2-oxa-phospholane based on methyldichlorophosphine, 
acrylic acid and acetic acid 
A mixture of 72 g (1 mole) of acrylic acid and 60 g (1 mole) of glacial 
acetic acid is added dropwise at 25.degree.-30.degree. C. to 117 g (1 
mole) of methyl-dichlorophosphine. After termination of the dropwise 
addition, the reaction solution is heated to 60.degree.-100.degree. C., 
while acetyl chloride (57 g) is distilled off and a strong current of 
hydrogen chloride is discharged. In order to eliminate the residual 
quantities of hydrogen chloride, the reaction mixture is heated under 
water jet vacuum to an internal temperature of 150.degree. C. The crude 
phospholane is purified by high vacuum distillation. 98 g of 
2-methyl-2,5-dioxo-1,2-oxa-phospholane (boiling point.sub.1,5 : 
169.degree. C.) are obtained, representing a yield of 73% of the 
theoretical yield. 
EXAMPLE 3 
2-methyl-2,5-dioxo-1,2-oxa-phospholane based on methyldichlorophosphine, 
acrylic acid and propionic acid 
A mixture of 36 g (0.5 mole) of acrylic acid and 37 g (0.5 mole) of 
propionic acid is added dropwise at 20.degree.-30.degree. C. to 58.5 g 
(0.5 mole) of methyldichlorophosphine. After termination of the dropwise 
addition the reaction solution is heated to 80.degree.-130.degree. C., 
while propionic acid chloride (36 g) is distilled off and hydrogen 
chloride discharged. Subsequently heating takes place under water jet 
vacuum to 150.degree.-160.degree. C. so as to eliminate the residual 
quantities of hydrogen chloride. After high vacuum distillation of the 
crude phospholane 47 g of 2-methyl-2,5-dioxo-1,2-oxa-phospholane (boiling 
point at 0.7 mm Hg: 160.degree.-162.degree. C.) are obtained, 
corresponding to a yield of 70% of the theoretical yield. 
EXAMPLE 4 
2-methyl-2,5-dioxo-1,2-oxa-phospholane based on methyldichlorophosphine, 
acrylic acid and propane-sulfonic acid 
A mixture of 36 g (0.5 mole) of acrylic acid and 62 g (0.5 mole) of 
propane-sulfonic acid is added dropwise to 58.5 g (0.5 mole) of 
methyldichlorophosphine at 20.degree.-30.degree. C. After termination of 
the dropwise addition, the temperature is slowly increased to 100.degree. 
C., while hydrogen chloride is discharged. Subsequently, propane-sulfonic 
acid chloride (18 g) of distilled off under water jet vacuum at an 
internal temperature of from 120.degree.-160.degree. C. The high vacuum 
distillation of the residue yields 51 g of 
2-methyl-2,5-dioxo-1,2-oxa-phospholane (boiling point at 2 mm Hg: 
185.degree.-190.degree. C.), representing a yield of 76.4% of the 
theoretical yield. 
EXAMPLE 5 
2-methyl-2,5-dioxo-1,2-oxa-phospholane based on methyldichlorophosphine, 
acrylic acid and methyl-ethyl-phosphinic acid 
A mixture of 36 g (0.5 mole) of acrylic acid and 54 g (0.5 mole) of 
methyl-ethyl-phosphinic acid is added dropwise at 20.degree.-30.degree. C. 
to 58.5 g (0.5 mole) of methyldichlorophosphine. After termination of the 
dropwise addition, the temperature is slowly increased to 
100.degree.-120.degree. C., while hydrogen chloride is discharged. 
Subsequently 40 g of methyl-ethyl-phosphinic acid-chloride are distilled 
off under water jet vacuum at an internal temperature of 
130.degree.-170.degree. C. The high vacuum distillation of the residue 
yields 47 g of 2-methyl-2,5-dioxo-1,2-oxa-phospholane (boiling point at 
1.3 mm Hg: 165.degree.-168.degree. C.), corresponding to a yield of 70% of 
the theoretical yield. 
EXAMPLE 6 
2-methyl-2,5-dioxo-1,2-oxa-phospholane based on methyldichlorophosphine, 
acrylic acid and methyl-ethyl-phosphinic acid-anhydride 
A mixture of 36 g (0.5 mole) of acrylic acid and 99 g (0.5 mole) of 
methyl-ethyl-phosphinic acid-anhydride is added dropwise to 58.5 g (0.5 
mole) of methyldichloro-phosphine at 20.degree.-40.degree. C. After 
termination of the dropwise addition stirring takes place for 15 minutes 
at 80.degree.-100.degree. C. Subsequently, 98 g of methyl-ethyl-phosphinic 
acid-chloride are distilled off under water jet vacuum at an internal 
temperature of 120.degree.-160.degree. C. The high vacuum distillation of 
the residue yields 49 g of 2-methyl-2,5-dioxo-1,2-oxa-phospholane, 
corresponding to a yield of 73% of the theoretical yield. 
EXAMPLE 7 
2-methyl-2,5-dioxo-1,2-oxa-phospholane based on methyldichlorophosphine, 
acrylic acid and methyl-ethyl-phosphinic acid-isobutyl ester 
A mixture of 36 g (0.5 mole) of acrylic acid and 76 g (0.5 mole) of 
methyl-ethyl-phosphinic acid-isobutyl ester is added dropwise to 58.5 g 
(0.5 mole) of methyldichloro-phosphine at 25.degree.-50.degree. C. After 
termination of the dropwise addition approximately 30 g of isobutyl 
chloride are distilled off under normal pressure. Subsequently, 
methyl-ethyl-phosphinic acid-chloride (about 26 g) is distilled off under 
water jet vacuum up to an internal temperature of from 
150.degree.-170.degree. C. The residue is submitted to a high vacuum 
distillation. 51 g of 2-methyl-2,5-dioxo-1,2-oxa-phospholane (boiling 
point at 0.6 mm Hg: 158.degree. C.) are obtained, corresponding to 76.4% 
of the theoretical yield. 
EXAMPLE 8 
2,4-dimethyl-2,5-dioxo-1,2-oxa-phospholane based on 
methyldichloro-phosphine methacrylic acid and 
3-hydroxypropyl-methyl-phosphinic acid 
A mixture of 43 g (0.5 mole) of methacrylic acid and 69 g (0.5 mole) of 
3-hydroxypropyl-methyl-phosphinic acid is added to 58.5 g (0.5 mole) of 
methyldichloro-phosphine at 50.degree.-60.degree. C., while hydrogen 
chloride is discharged. Subsequently heating takes place under water jet 
vacuum to an internal temperature of up to 150.degree. C. The residue is 
distilled under reduced pressure. 35 g of 
2-methyl-2-oxo-1,2-oxa-phospholane (boiling point at 1.5 mm Hg: 
120.degree.-130.degree. C.) and 55 g of 
2,4-dimethyl-2,5-dioxo-1,2-oxa-phospholane (boiling point at 0.7 mm Hg: 
150.degree.-155.degree. C.) are obtained. The yield in 
2,4-dimethyl-2,5-dioxo-1,2-oxa-phospholane represents 71% of the 
theoretical yield. 
EXAMPLE 9 
2-methyl-2,5-dioxo-1,2-oxa-phospholane based on methyldichloro-phosphine 
acrylic acid and 3-hydroxybutyric acid 
A mixture of 52 g (0.5 mole) of 3-hydroxy-butyric acid and 36 g (0.5 mole) 
of acrylic acid is added dropwise to 58.5 g (0.5 mole) of 
methyl-dichloro-phosphine at 25.degree.-30.degree. C., while hydrogen 
chloride is discharged. Subsequently 65 g of butyrolactone are distilled 
off under water jet vacuum up to an internal temperature of 180.degree. C. 
The residue is submitted to a vacuum distillation. At a boiling point at 
0.7 mm Hg: 173.degree.-175.degree. C. distillation yields 53 g of 
2-methyl-2,5-dioxo-1,2-oxa-phospholane, corresponding to a yield of 79% of 
the theoretical yield.