Process for obtaining bis(2,4-di-tert-butylphenyl) halophosphites

The invention relates to a process for obtaining phosphorus acid-bis(2,4-di-tert-butylphenyl) ester halides in which a phosphorus acid-2,4-di-tert-butylphenyl ester dihalide is heated in the presence of a catalyst containing nitrogen or phosphorus, or both, to 130.degree. C. to 280.degree. C. and the phosphorus trihalide produced by disproportionation is removed from the reaction mixture.

DESCRIPTION 
Bis(2,4-di-tert-butylphenyl) halophosphites are useful starting compounds 
for the preparation of phosphites (U.S. Pat. No. 4,739,000) or 
phosphonites (German Patent Applications P 38 43 016.9 and P 39 16 502.7) 
of industrial interest, which are used as stabilizers for synthetic 
polymers. 
It is known from U.S. Pat. No. 4,739,000 that bis(2,4-di-tert-butylphenyl) 
chlorophosphite can be prepared by the reaction of phosphorus trichloride 
with twice the molar amounts of 2,4-di-tert-butylphenol and triethylamine 
to neutralize the hydrochloric acid liberated. In this process, the use of 
considerable amounts of a suitable aprotic solvent such as toluene is 
naturally unavoidable. The final product, according to the information 
there, has a purity of 85%. 
For intended industrial production, such a procedure is particularly 
unfavorable, because not only do considerable amounts of solvents have to 
be worked up again, but the triethylammonium chloride formed also has to 
be neutralized with an alkali metal hydroxide solution in order to recover 
the base used as auxiliary. A forced yield of 2 equivalents of salt cannot 
be avoided in this case. 
The preparation of diaryl halophosphites by direct reaction of phenols or 
naphthols and phosphorus trihalides in the molar ratio 2:1 is 
unsatisfactory because of disproportionation reactions and secondary 
reactions which cannot be controlled (Houben-Weyl, "Methoden der 
Organischen Chemie", [Methods of Organic Chemistry], E1, p. 373, 1982, see 
also Zh. Obsch. Khim. 37, 464-468, 1967). 
The object of the present invention was therefore to obtain 
bis(2,4-di-tert-butylphenyl) halophosphites in a simple manner. 
To achieve this object, the invention proposes a process for obtaining 
bis(2,4-di-tert-butylphenyl) halophosphites of the formula 
##STR1## 
in which X is a halogen having an atomic weight of at least 35, preferably 
chlorine or bromine, in particular chlorine, which is characterized in 
that a 2,4-di-tert-butylphenyl dihalophosphite of the formula (II) 
##STR2## 
is heated to 130.degree. to 280.degree. C. in the presence of a 
catalytically active compound containing nitrogen and/or phosphorus and 
the phosphorus trihalide formed in this way by disproportionation is 
removed from the reaction mixture. 
According to a particularly preferred embodiment, a procedure is used in 
which, by addition of a less than stoichiometric amount of 
2,4-di-tert-butylphenol, additional bis(2,4-di-tert-butylphenyl) 
halophosphite is produced. 
The process according to the invention is not affected by the disadvantages 
which are associated with the known process. 
The reaction, which can be carried out per se in any conceivable manner, is 
preferably carried out without the use of a solvent, although it can also 
be carried out with a solvent which is used as an azeotropic entraining 
agent. Advantageously, the dihalophosphorous acid monoester (II) is 
reacted with up to 0.9, preferably 0.3 to 0.6, equivalents of 
2,4-di-tert-butylphenol and the mixture is heated in the presence of the 
catalyst to 130.degree.-280.degree. C. In this process, it is particularly 
advantageous, after completion of the evolution of hydrogen halide, to 
additionally carry out a sufficiently long afterreaction in the 
abovementioned temperature range, the content of (II) being reduced in 
favor of the product (I) by disproportionation processes without undesired 
by-products being formed to a noticeable extent. To isolate the desired 
product (I), residual starting material (II) is then distilled off under 
reduced pressure. In this process, the catalyst is usually also carried 
off. 
Preferably, the reaction is carried out at temperatures from 160.degree. to 
230.degree. C. The reaction is in general complete, depending on the 
temperature used, after 2 to 10 hours. The reaction is usually carried out 
in the course of 2 to 5 hours. 
Generally, the reaction is carried out under normal pressure; however, it 
may sometimes be advantageous to favor the removal of the hydrogen 
chloride by the use of reduced pressure. 
As the reactants are sensitive to hydrolysis, the reaction is 
advantageously carried out with exclusion of moisture. It may be 
advantageous to carry out the reaction while passing through inert gas 
such as nitrogen or argon or under a protective gas atmosphere of these 
gases. 
The catalyst is usually employed in small amounts, for example 0.0001 to 
0.1 mol, preferably 0.001 to 0.02 mol per mole of (II). 
Preferably, the catalysts employed according to the invention are 
a) compounds of the formulae (III), (IV), (V) or (VI) 
##STR3## 
in which Y is an element of the fifth main group of the Periodic Table 
according to Meyer-Mendeleev having an atomic number from 7 to 15 (i.e. 
nitrogen or phosphorus), A is an inorganic or organic acid radical, 
preferably a halide, sulfate or sulfonate, R.sup.1, R.sup.2, R.sup.3 and 
R.sup.4 are identical or different organic radicals, preferably of 
(cyclo)aliphatic or aromatic character, having up to 20 carbon atoms, 
preferably 1 to 10 carbon atoms, where two of the radicals R.sup.1 to 
R.sup.4 or, in the case of the formula (VI), two or three of the radicals 
R.sup.1 to R.sup.3 can close to give a cyclic, optionally substituted 
system, if appropriate with the inclusion of a heteroatom such as oxygen, 
nitrogen or sulfur, and Z is oxygen or--if Y is phosphorus --alternatively 
sulfur, two halogen atoms or the group NR.sup.5, where R.sup.5 is R.sup.1 
or hydrogen, 
b) acid amides and/or 
c) compounds from the group comprising mono- to tribasic, organic or 
inorganic fully amidated acids of tri- or pentavalent phosphorus, whose 
nitrogen atoms are alkyllated by aliphatic radicals having up to 20 carbon 
atoms, preferably 1 to 10 carbon atoms, and whose organic radicals can 
contain up to 20 carbon atoms, preferably 1 to 10 carbon atoms. 
Examples of suitable catalysts are: 
A. Tertiary aliphatic and aromatic amines and phosphines such as 
trimethyl-, triethyl-, tripropyltriisopropyl-, tributyl-, tri-n-hexyl-, 
tris(2-ethylhexyl)- and triphenylamine, trimethyl-, triethyl-, tripropyl-, 
tributyl-, triphenyl- and tris(p-dimethylaminophenyl)phosphine and the 
corresponding mixed amines, phosphines, phospholanes and phospholenes such 
as dimethylethylamine, diethylbutylamine, N-dimethylaniline, 
4-methyl-N-dimethylaniline, N-diethylaniline, 
bis-(1,8-dimethylamino)naphthalene, N,N'-tetramethylphenylenediamine or 
N-methylpyrrolidine; methyldiethylphosphine,dimethylpropylphosphine, 
diethylbenzylphosphine,1-methyl-3-phospholene and 
1-ethyl-3-methyl-3-phospholene; 
B. Azomethines such as hydrobenzamide, benzylideneaniline, o-, m- and 
p-methyl-, o-, m- and p-methoxyo-, m- and p-chlorobenzylideneaniline and 
corresponding derivatives of substituted anilines such as of o-, m- and 
p-toluidine, of o-, m- and p-nitroaniline, of o-, m- and p-anisidine and 
of o-, m- and p-chloroaniline; 
C. Quaternary ammonium salts or phosphonium salts such as 
tetramethylammonium chloride or bromide, tetraethylphosphonium chloride, 
trimethyl- or triethylbenzylammonium chloride or bromide, 
trimethylbenzylphosphonium chloride, 
triphenylethylphosphonium-2,4-diaminobenzene sulfonate; 
D. Heterocyclic compounds having aromatic character such as pyridine, 
quinoline, their various alkyl and dialkyl, preferably methyl or dimethyl 
derivatives, dimethylaminopyridines,imidazole,N-vinylimidazole, 
benzothiazole, 2-amino-6-ethoxybenzothiazole, and also phosphabenzoles; 
E. Acid amides such as dimethylformamide, diethylformamide, 
N-dimethylacetamide, N-diethylpropionamide, N-dimethylbenzamide, 
N-methylpyrrolidone, N,N'-tetramethylterephthalamide or ureas such as 
tetramethylurea and trimethylphenylurea; 
F. Other nitrogen and/or phosphorus compounds having a higher valency of a 
nitrogen or phosphorus atom than 3, such as pyridine-N-oxide, trimethyl-, 
tributyl-, trihexyl-, triphenyl-, and dimethylphenylphosphine oxide and 
dimethylchloromethyl-, dimethyleicosyl-, dimethyldodecyl-, dimethyl- and 
dimethylpyrrolidinyl-1-methylphosphine oxide, triphenylphosphine 
dichloride, dimethylphenylphosphine sulfide, dimethyldodecylphosphine 
sulfide, triphenylphosphine imine, dimethylchloromethylphosphine 
dichloride, N-2-dimethylphosphinylethylmethylacetamide, 
N-2-dimethylphosphinylcthylmethylamine, phospholeneoxides or phospholane 
oxides, such as 1-methylphospholene-1-oxide and 
1-ethyl-3-methylphospholene-1-oxide or 1-methylphospholane-1-oxide and 
1-ethyl-3-methylphospholane-1-oxide; 
G. Amides of phosphinous and phosphonous acid and of phosphinic and 
phosphonic acids and their thio analogs, such as ethanephosphonic acid 
bisdiethylamide, methanebutanephosphinous acid dimethylamide, 
diethylphosphinous acid isobutylamide, and also triamides of phosphoric 
acid and thiophosphoric acid, such as hexamethylphosphoric triamide. 
Mixtures of catalysts of this type can also be employed. 
The 2,4-di-tert-butylphenyl dihalophosphites (II) required as starting 
substances are known from the literature and can be prepared in a simple 
manner by the process described in German Application P 39 28 291.0 by 
reaction of PX.sub.3 (X=Cl, Br) with 2,4-di-tert-butylphenol. The starting 
substances thus obtained can be used directly for the present process. 
Prior distillation is not necessary. 
The reaction product is usually obtained in yellow viscous form. As the 
main constituent, it contains bis(2,4-di-tert-butylphenyl) halophosphite 
of the formula (I) in which the content of (I) actually also depends on 
the chosen ratio of the reactants, the reaction temperature and the 
reaction time. For working-up, unreacted starting material (II) can be 
removed by distillation under reduced pressure. The residue then in 
general has a content of 83 to 97% (according to .sup.31 P-NMR analysis) 
of (I). If it is desired to react the product (II) with Grignard 
compounds, as is described in German Patent Applications P 38 43 016.9 and 
P 39 16 502.7, in order to prepare stabilizers for polymers, then a 
further purifification is not necessary. If desired, the products (I), 
however, can be further purified by distillation under reduced pressure. 
It is particularly suprising that, by the process according to the 
invention, diaryl monohalophosphites are available in such a high yield, 
since it is known from the literature that an equilibrium is established 
with such compounds in the temperature range used as a result of 
diproportionations, a complex mixture of various products having a very 
high content of triaryl phosphites being formed (for example Zh. Obsch. 
Khim. Vol. 37, 464-468, 1967). In order to suppress such reactions, a 
preferred temperature range of 5.degree. to 100.degree. C. is also given 
in U.S. Pat. No. 4,739,000 for the preparation of (I) (with X=Cl). In the 
present case, the formation of a particularly high proportion of 
tris(2,4-di-tert-butylphenyl) phosphite was therefore also to be expected, 
because the catalysts used, as is known, catalyze the formation of this 
by-product, which is undesired in this case (see German 
Offenlegungsschrift 2,940,620). 
In the following examples, the content information relates to the 
percentage of total phosphorus according to .sup.31 P-NMR analysis.

EXAMPLES 
1) A mixture of 768 g (2.5 mol) of 2,4-di-tert-butylphenyl 
dichlorophosphite, 258 g (1.25 mol) of 2,4-di-tert-butylphenol and 0.2 g 
of 4-dimethylaminopyridine (=1.6 mmol) was heated to about 180.degree. C. 
with exclusion of moisture and under a nitrogen atmosphere for 5 hours, a 
strong evolution of hydrogen chloride taking place at the beginning. The 
mixture was then allowed to cool to 100.degree. C. and unreacted 
dichlorophosphorous acid ester and low-boiling components were distilled 
off under reduced pressure until the internal temperature was 200.degree. 
C. In the course of this, about 200 g of distillate were obtained. The 
clear yellow distillation residue had a content of about 88% of 
bis(2,4-di-tert-butylphenyl) chlorophosphite; .delta. CDCl.sub.3 =160.5 
ppm. 
2) The reaction was carried out as in Example 1, but at 140.degree. C. 
About 280 g of unreacted starting material were recovered. The 
distillation residue contained about 85% of bis(2,4-di-tert-butylphenyl) 
chlorophosphite. 
3) As in Example 1, 614.4 g (=2 mol) of 2,4-di-tertbutylphenyl 
dichlorophosphite and 206.3 g (=1 mol) of 2,4-di-tert-butylphenol were 
reacted in the presence of 1 g (0.012 mol) of pyridine. 240 g of starting 
compound were recovered. The distillation residue contained about 90% of 
bis(2,4-di-tert-butylphenyl) chlorophosphite. 
4) The mixture of 921.6 g (3 mol) of 2,4-di-tert-butylphenyl 
dichlorophosphite and 0.3 g (=2.4 mmol) of 4-dimethylaminopyridine was 
stirred for 5 hours at 190.degree.-200.degree. C. with exclusion of 
moisture and while passing through a gentle stream of nitrogen. During 
this time, about 165 g of phosphorus trichloride distilled off. The 
mixture was then allowed to cool to about 100.degree. C. and was distilled 
under reduced pressure and with renewed heating until the bath temperature 
was 200.degree. C., whereupon about 190 g of virtually pure 
2,4-di-tert-butylphenyl dichlorophosphite distilled over. 
The yellow viscous distillation residue had a content of about 97% of 
bis(2,4-di-tert-butylphenyl) chlorophosphite; .delta. CDCl.sub.3 =160.5 
ppm. 
5) The mixture of 92.2 g (=0.3 mol) of 2,4-di-tert-butylphenyl 
dichlorophosphite and 0.1 g (=0.9 mmol) of 4-dimethylaminopyridine was 
stirred for 6 hours at 190.degree. C. while passing through a gentle 
stream of nitrogen. In the course of this, PCl.sub.3 formed was carried 
off. The mixture was allowed to cool, the distillative removal of residual 
starting material was dispensed with and an .sup.31 P-NMR spectrum was 
prepared. The residual product contained about 70% of 
bis(2,4-di-tert-butylphenyl) chlorophosphite. 
6) The reaction was carried out as in Example 4 with the difference that 
0.1 g (0.5 mmol) of tri-n-butylphosphine was used as the catalyst. The 
residual product contained about 50% of bis(2,4-di-tert-butylphenyl) 
chlorophosphite. 
COMISON EXPERIMENT TO EXAMPLES 5 AND 6 
In an experiment carried out under the same conditions, but without 
addition of catalysts, the content of bis(2,4-di-tert-butylphenyl) 
chlorophosphite after the same reaction time was only about 4%.