2,4,4'-Trimethylpentyl, cyclohexylphosphinic acid and its preparation

Free Radical Addition of Mono 2,4,4'-trimethylpentylphosphine to cyclohexene followed by the oxidation of the 2,4,4'-trimethylpentyl, cyclohexylphosphine with two moles of hydrogen peroxide is employed to prepare 2,4,4'-trimethylpentyl, cyclohexylphosphinic acid. The 2,4,4'-trimethylpentyl, cyclohexylphosphinic acid is useful as a cobalt extractant.

The invention relates to 2,4,4'-trimethylpentyl, cyclohexylphosphinic acid, 
i.e., 
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and a method for the production thereof which comprises free radical 
addition of mono 2,4,4'-trimethylpentylphosphine to cyclohexene followed 
by the oxidation of the 2,4,4'-trimethylpentyl, cyclohexylphosphine with 
two moles of hydrogen peroxide. The end product, either as an acid or in 
its salt form, finds utility as a cobalt extractant and, more 
specifically, as a selective extractant for cobalt (II) in aqueous cobalt 
(II)--bearing solutions containing nickel (II). 
In the preparation of this compound free radical initiators of the azobis 
type are preferred although others, such as the peroxides, may be used. 
Azobisobutrylnitrile is the most preferred. The temperature range of the 
reaction is directly related to the half life of the initiator employed. 
For azobisbutrylnitrile the temperature range should be about 
40.degree.-110.degree. C., preferably 60.degree. to 90.degree. C. The mole 
ratio of olefin to mono alkylphosphine can vary from 0.1 to 10 depending 
on the relative rates of formation of the di- and tri-alkylphosphines. 
Preferably the range is between 0.5 to 3. 
In the oxidation stage, the oxidation of the dialkylphosphine to the 
dialkylphosphine oxide is exothermic and takes place readily at 
30.degree.-100.degree., preferably for this first oxidation step at 
50.degree.-70.degree. C. To convert the dialkylphosphine oxide to the 
dialkylphosphine acid, the temperature should be increased to within 
50.degree. to 120.degree. C., preferably 80.degree. to 100.degree. C. 
Higher temperatures tend to remove one alkyl group forming some 
monoalkylphosphonic acid. At lower temperatures the oxidation is rather 
slow and excessive reaction times may be required.

Whereas the exact scope of the instant invention is set forth in the 
appended claims, the following specific examples illustrate certain 
aspects of the present invention, and, more particularly, point out 
methods of evaluating the same. However, the examples are set forth for 
illustration only and are not to be construed as limitations on the 
present invention except as set forth in the appended claims. All parts 
and percentages are by weight unless otherwise specified. 
EXAMPLE 1 
500 Parts of 09.5% mono 2,4,4'trimethylpentylphosphine is charged along 
with 482 parts of cyclohexene to a 1 gallon autoclave. 15 parts of 
azobisobutrylnitrile (VAZO 64.RTM.) is added and the mixture quickly 
heated to 60.degree. C. The temperature is then slowly raised from 
60.degree. C. to 87.degree. C. over a 51/2 hour period. 
The product contained 39.36% cyclohexene, 22.70% mono 2,4,4' 
trimethylpentylphosphine, 35.26% 2,4,4' trimethylpentyl, 
cyclohexylphosphine, and 0.35% 2,4,4' trimethylpentyl, 
dicyclohexylphosphine. 
A further 20 parts of azobisobutrylnitrile is added to the mixture. It is 
heated quickly to 60.degree. C. and then slowly from 60.degree. C. to 
89.degree. over a 61/2 hour period. 
The product contained 34.39% cyclohexene 11.14% mono 
2,4,4'trimethylpentylphosphine, 48.3% 2,4,4' trimethylpentyl, 
cyclohexylphosphine, and 2.18% 2,4,4' trimethylpentyl 
dicyclohexylphosphine. 
The product mixture is then distilled to remove the cyclohexene and mono 
2,4,4'trimethylpentylphosphine. 516.9% of the residue containing 0.45% 
mono 2,4,4'trimethylpentylphosphine, 90.0% 2,4,4'trimethylpentyl 
cyclohexylphosphine and 3.48% 2,4,4' trimethylpentyl, 
dicyclohexylphosphine is placed in a stirred, heated resin flask under an 
inertr atmosphere. The mixture is heated to 50.degree. C. and 575 mL of 
24% H.sub.2 O.sub.2 is added slowly with stirring over 11/2 hours. During 
that time the temperature rose from 50.degree. C. to 98.degree. C. To 
completely oxidize all the dialkylphosphine to the phosphinic acid, an 
additional 500 g of 24% H.sub.2 O.sub.2 is added and the mixture heated 
for a further 5 hours at 100.degree. C. 
The product is then decanted as a viscous oil. It assayed 85.97% phosphinic 
acid but also contained 9.58% mono 2,4,4' trimethylpentylphosphonic acid. 
During the severe oxidation conditions, a portion of the cyclohexyl groups 
were removed and the resulting 2,4,4' trimethylpentylphosphine is oxidized 
to 2,4,4' trimethylpentylphosphonic acid. 
Most of the phosphonic acid is removed by scrubbing with 0.1 N NaOH and 
water. The final product assayed 85.37% 2,4,4' trimethylpentyl, 
cyclohexylphosphinic acid and 4.86% 2,4,4' trimethylpentylphosphonic acid. 
The product is a viscous oil and had a pKa of 6.04 in 75% isopropanol. The 
.sup.31 P NMR chemical shift in toluene is -53.13 ppm with respect to 85% 
H.sub.3 PO.sub.4. 
EXAMPLE 2 
The following example illustrates the ability of 2,4,4'-trimethylpentyl, 
cyclohexyl phosphinic acid to separate cobalt (II) from nickel (II). 
The 2,4,4'-trimethylpentyl, cyclohexylphosphinic acid is dissolved in an 
aliphatic petroleum diluent (Solvesso.RTM. 100) modified with 5% v/v 
isoderanol to obtain a concentration of 15% by volume, then a 
predetermined amount of 28% ammonium hydroxide is added to adjust the pH. 
An aliquot (50 mls) is shaken at 50.degree. C. for 5 minutes at 50.degree. 
C. with an equal volume of an aqueous solution containing 2.05 gpl of 
cobalt (II) and 102.4 gpl of nickel (II), respectively, as sulfate salts, 
to extract the cobalt (II) into the organic phase. The aqueous phase is 
then separated from the organic phase and analyzed for cobalt (II) 
content. Based on the results obtained, the percent cobalt (II) extracted 
is calculated by mass balance. The percent nickel (II) extracted is 
determined by analyzing the organic phase. The results obtained are shown 
in Table I. 
TABLE I 
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% Metal Extraction 
Co/Ni Separation 
Equilibrium 
Co Ni Factor pH 
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85.1 0.78 726 4.70 
95.6 1.66 1274 5.18 
98.4 3.19 1910 5.53 
99.9 4.64 21030 5.80 
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