Purification of phosphorous acid esters

Process for the purification of phosphoric acid partial ester mixtures in which, after the addition of a basic, non-volatile inorganic or organic compound, the unreacted fatty alcohol is directly removed from the partial ester mixture by distillation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
This invention relates to the purification of phosphoric acid partial ester 
mixtures produced by reaction of fatty alcohols with phosphorus pentoxide. 
2. Statement of Related Art: 
Among the phosphoric acid esters produced worldwide, the mixtures of mono- 
and dialkyl derivatives obtained by reaction of phosphorus pentoxide with 
alcohols are predominant. 
The reaction mechanism has not yet been definitively elucidated. Similarly, 
the summation formula currently postulated for phosphorus pentoxide, 
namely -P.sub.4 O.sub.10 -, is not yet certain. 
T. Fay, G. P. Sheridan and D. R. Karsa, Kommittee Espanol dea Detergentes, 
XII. Jornado (1981), point out that the phosphorus pentoxide normally 
marketed contains large amounts of high-polymer material and, accordingly, 
should retain the formula P.sub.2 O.sub.5. 
In the production of phosphoric acid esters, especially by reaction of 
fatty alcohols with phosphorus pentoxide, the products contain varying 
amounts-depending on the molar reaction ratio of unreacted alcohol which, 
in many cases, affects the use of the products and is therefore almost 
always undesirable. The removal of the free alcohol is only possible by 
complicated, timeconsuming measures. 
K. Sasse in "Houben-Weyl", Vol. 12, "Organische Phosphorverbindungen 
(Organic Phosphorus Compounds)", Part 2, pages 156 et seq describes the 
formation of phosphoric acid partial esters by the action of alcohols on 
phosphorus pentoxide. The free phosphoric acid is normally separated from 
the reaction product via the barium salts or, where relatively long-chain 
alcohols are used, via the sodium salts. The phosphorylation of sugars 
with phosphorus pentoxide is carried out at elevated temperature in the 
presence of tertiary amines. 
Direct separation of the free alcohol by distillation is complicated by the 
elimination of olefins from the esters. In the case of short-chain 
alcohols, olefin formation actually becomes the main reaction. Chemical 
Abstracts, 95, 22 1704 w describes the neutralization of aliphatic 
phosphoric acid esters with an aqueous alkanolamine solution and 
subsequent extraction of the nonionic material with a low-boiling 
paraffin. 
Published German Application 33 25 337 describes a process for the 
production of phosphoric acid diesters in which a base is added to the 
partial ester mixture in a quantity of from 0.5 to 1.3 equivalents, based 
on the phosphorus atoms in the mixture. The phosphoric acid monoesters are 
converted into o-phosphoric acid and organic hydroxyl compounds by 
hydrolysis in aqueos solution and, after the reaction step, are removed by 
distillation in the case of low-boiling alcohols or by fractional 
crystallization in the case of relatively long-chain alcohols. Phosphoric 
acid diesters which may still contain free unreacted alcohol are obtained. 
STATEMENT OF THE INVENTION 
Other than in the operating examples, or where otherwise indicated, all 
numbers expressing quantities of ingredients or reaction conditions used 
herein are to be understood as modified in all instances by the term 
"about". 
An object of the present invention is to provide a simple process which 
enables the alcohol still present in phosphoric acid ester mixtures to the 
removed without decomposition of the esters formed. It has now 
surprisingly been found that there is virtually no formation of oelfins if 
small quantities (0.05 to 0.2 mol equivalents, based on the quantity of 
phosphorus atoms in the mixture) of a basic, non-volatile inorganic or 
organic compound are added to the partial ester mixture before or 
preferably after the reaction and the unreacted fatty alcohol is directly 
removed from the mixture by distillation. In this way, the thermal 
stability of the phosphoric acid esters is so comprehensively increased 
that even relatively long-chain fatty alcohols can be removed from the 
mixture by distillation. The thermal stability of the phosphoric acid 
esters is still intact even at temperatures of from 180.degree. to to 
200.degree. C. 
The present invention provides a process for the purification of phosphoric 
acid partial esters which are produced in known manner by reaction of a 
fatty alcohol or fatty alcohol mixture with phosphorus pentoxide. Fatty 
alcohols in the context of the invention are C.sub.6 -C.sub.18 saturated 
or unsaturated alcohols and, more particularly, straight-chain or 
branched-chain C.sub.8 -C.sub.12 alcohols. Fatty alcohols according to the 
invention are selected from the group comprising hexyl alcohol, 
2-ethylhexyl alcohol, heptyl alcohol, octyl alcohol, nonyl alcohol, 
isononyl alcohol, decyl alcohol, isodecyl alcohol, undecyl alcohol, 
dodecyl alcohol, tridecyl alcohol, isotridecyl alcohol, tetradecyl 
alcohol, pentadecyl alcohol, hexadecyl alcohol, heptadecyl alcohol, 
octadecyl alcohol, oleyl alcohol, elaidyl alcohol and isostearyl alcohol. 
In view of the high boiling points of the alcohols used, the distillation 
is preferably carried out at reduced pressure. More preferably, the 
distillation is carried out at 0.1 to 50 mbar. 
The basic (i.e. alkaline) non-volatile, inorganic or organic compounds 
added to the partial ester mixture in quantities of from 0.05 to 0.2 mol 
equivalents, based on the phosphorus atoms in the mixture, are selected 
from alkali metal hydroxides, such as potassium hydroxide and sodium 
hydroxide, and alkanolamines and amines with molecular weights in the 
range of from 129 to 297. By "non-volatile" is meant not volatile under 
the reaction conditions employed in the practice of the invention. 
Examples of alkanolamines and amines in the above molecular weight range 
include diethanolamine, dimethyl cocosamine, cocosamine, tributylamine and 
N-lauryldiaminopropane. 
The basic compounds are preferably added to the partial ester mixtures in 
quantities of 0.1 mol equivalent, based on the phosphorus atoms in the 
mixture. 
The advantages of the present invention become clear on analysis of the 
distillate. Without the addition of the basic, nonvolatile compounds 
according to the invention, the quantities of distillate are increased in 
relation to the process of the invention. In addition, without the 
addition of the basic, nonvolatile compounds, the iodine value of the 
distillate is increased by a factor of at least ten. 
The invention will be illustrated but not limited by the following examples 
.

EXAMPLES 
Example A 
594.0 g (4.5 moles) n-octanol (OH value 424) were introduced into heated in 
a 1000 ml three-necked flask equipped with a stirrer and thermometer. At a 
temperature of 50.degree. to 60.degree. C., 213.0 g (1.5 moles) phosphorus 
pentoxide were uniformly added over a of 2 h using a hermetically sealed 
powder dispenser. The mixture was then left to react for 2 h at 90.degree. 
C. After addition of 31 g water, the mixture was stirred for another 3 h 
at 90.degree. C. 
837 g of a colorless oil was obtained. Analysis (passage over an ion 
exchanger) revealed a content of 7.8% unreacted alcohol. 
Example 1 
16.6 g (0.07 mole) dimethyl cocosamine were added to 200.0 g (0.72 
equivalent P) of the phosphoric acid ester obtained in accordance with 
Example A, followed by distillation in vacuo. The mixture was heated to a 
sump temperature of 170.degree. C. under a pressure of 20 mbar. 15.2 g 
distillate having an iodine value of 1.6 were obtained. 199.8 g of an 
almost colorless residue containing 0 2% n-octanol remained in the flask. 
Under the same conditions, the following results were obtained: 
______________________________________ 
Distillate Residue 
Ex- quantity quantity 
ample Addition Mol/P (g) IV. (g) 
______________________________________ 
2 potassium hydroxide 
0.1 14.8 1.3 187.9 
3 diethanolamine 
0.2 14.1 1.1 186.3 
4 cocosamine 0.2 13.8 1.5 208.1 
5 tributylamine 0.1 13.1 1.4 194.4 
6 N--lauryldi- 0.1 14.9 3.1 193.7 
aminopropane 
______________________________________ 
Comparison Example 1 
200.0 g of the phosphoric acid ester obtained in accordance with Example A 
were also subjected to the distillation treatment in vacuo in the absence 
of an addition according to the invention. 
After only 23.8 g distillate had accumulated, heating was stopped although 
distillation was not yet over. Analysis of the distillate revealed an 
iodine value of 15; the quantity of residue amounted to 175.2 g for a 
residual content of 2.4% n-octanol. 
Example B 
231.0 g (1.75 moles) n-octanol (OH value 425) were reacted with 71.0 g (0.5 
mole) phosphorus pentoxide in a 500 ml three-necked flask equipped as in 
Example 1. The reaction temperature during the 2-hour addition was 80 to 
90.degree. C. After stirring for 2 h at 100.degree. C., 11.1 g water were 
added, followed by stirring for another 3 h. 
312g of a yellowish colored oil still containing 14.8% n-octanol were 
obtained. 
Example 7 
30.4 g (0.2 mol/P) dimethyl cocosamine were added to 200.0 g of the 
phosporic acid ester obtained in accordance with Example B, followed by 
vacuum distillation at 20 mbar to remove the unreacted alcohol. The 
maximum sump temperature was 172.degree. . In all, 28.8 g distillate 
having an iodine value of 2.0 were formed. 
Comparison Example 2 
200.0 g of the ester obtained in accordance with Example B were treated as 
in Example 7 without the addition of dimethyl cocosamine. 34.2 g 
distillate having an iodine value of 46.3 were formed. 
Example C 
780 g (6 moles) 2-ethyl hexanol were reacted with284 g (2moles) phosphorus 
pentoxide at 50.degree. to 60.degree. C. in a 2-liter three-necked flask 
equipped as in Example A. After stirring for 2 hours, 36 g water were 
added and the mixture treated therewith for 3 hat 90.degree. C. 
1103g of a yellowish liquid still containing 13% unreacted alcohol were 
obtained. 
Example 8 
0.2 mole potassium hydroxide/P in the form of a 45% solution were added to 
550 g of the ester obtained in accordance with Example C. 
The free alcohol was distilled off under a pressure of 20 mbar up to a sump 
temperature of 160.degree. C. 
70.2 g distillate having an iodine value of 1.2 were obtained. 
EXAMPLE D 
390 g (1.5 moles) tallow alcohol were reacted with 71 g (0.5 mole) 
phosphorus pentoxide at 60.degree. to 70.degree. C. in a 1-liter 
three-necked flask equipped as in Example A. After stirring for 2 h at 
70.degree. C., 10 g water were added and the mixture kept at 90.degree. C. 
for 3 h. 
471 g of a white mass solid at room temperature, which still contained 
18.1% unreacted alcohol, were obtained. 
Example 9 
200 g of the ester obtained in accordance with Example D were mixed with 
10.1 g (0.1 mole/P) dimethyl cocosamine and the resulting mixture passed 
through a thin-layer evaporator at 180.degree. C. under a pressure of 
10.sup.-1 bar. 
38.4 g distillate, iodine value 1.3, were obtained.