US2753368A

US2753368A - Higher alkyl esters of phosphonic acids

Info

Publication number: US2753368A
Application number: US365252A
Authority: US
Inventors: Forrest J Watson; Rupert C Morris; John L Van Winkle
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1950-11-13
Filing date: 1953-06-30
Publication date: 1956-07-03
Anticipated expiration: 1973-07-03

Description

United States Patent HIGHER ALKYL ESTERS 0F PHO'SPHONIC ACIDS Forrest J. Watson and Rupert C. Morris, Berkeley, and John L. Van Winkle, San Lorenzo, Caliii, assignors to Shell Development Company, Emeryville, Calif., a corporation of Delaware No Drawing. Original application November 13, 1950, Serial No. 195,456. Divided and this application June 30, 1953, Serial No. 365,252

8 Claims. or. 260-461) This invention relates to novel esters of phosphonic acids with branched-chain alkyl alcohols containing at least 8 carbon atoms in each of the alkyl groups, all of the alkyl groups in said esters being identical in structure. The present application is a continuation-in-part of copending application Serial No. 195,456, filed November 13, 1950, now abandoned.

The increasing complexity and greater precision of machinery employed in modern industry creates an evergrowing demand for compounds and compositions which will provide adequate lubrication for the moving parts of such machinery under all conditions of operating temperatures and pressures. It has been found that natural lubricating oils, whether employed alone or in combination with various additives, are not entirely suitable for certain types of applications. Therefore, a large number of synthetic lubricants have been prepared and tested. Many of these are suitable only for specialized.

applications; others find wider applicability, according to their nature and characteristics. Increasing interest has been shown regarding the use of various compounds containing phosphorus as lubricants for a Wide variety of applications. This interest has been based, for the most part, on the fact that many such phosphorus-containing compounds possess desirable lubricating characteristics, such as the ability to lubricate two surfaces, each moving in relation to the other at high speeds under extreme conditions of pressure and temperature. These compounds have some shortcomings as lubricants, however, for many of them cause an undesirable amount of corrosion of the alloys commonly employed as bearings in modern high-speed machinery. Particularly, it has been found that many phosphorus-containing compounds are highly corrosive with respect to the so-called hardmetal bearing alloys, such as copper-lead, cadmiumnickel and cadmium-silver alloys. In many cases, the corrosivity of the lubricant increases with the length of its use-due to decomposition of the lubricant. Such lubricants may cause corrosion to alloy bearings of the copper-lead type to the extent of mg./cm. and even,

greater when such bearings are submerged for hours or less in an air agitated oil which has been pre-oxidized at about 340 F. for 25 to 50 hours.

It is our discovery that certain novel esters of phosphonic acids with the same branched-chain alkyl alcohol containing at least 8 carbon atoms in the alkyl group possess highly desirable characteristics as lubricants and that such esters exhibit but a minimal amount of corrosivity toward the common hard-metal bearing alloys. Therefore, it is an object of the present invention to provide lubricants for modern industrial machinery that give excellent lubrication of bearing surfaces over a wide range of speeds, pressures and temperatures without causing excessive corrosion of the bearing alloys of that machinery. The novel compounds of the invention also possess great resistance to decomposition under oper- "ice.

ating conditions and provide continuous, dependable lubrication over an indefinite period of time.

The ester compounds of the present invention may be represented by the following general formula:

0 (R),.1 (oR),,.

where all the groups represented by R are identical in structure and are branched-chain hydrocarbon groups, each of which contains 8 or more carbon atoms. It is preferred that the hydrocarbon groups be alkyl groups containing from 8 to 15, inclusive, carbon atoms. The symbol m is a small integer selected from the group, 1 and 2, and the symbol It is a small integer, m and n always having the relationship m+n=3. Representative compounds falling within this group are: bis(2-ethylhexyl) Z-ethylhexanephosphonate, di(isooctyl) isooctane phosphonate, 2-ethylhexyl bis(2-ethylhexane)phosphonate, isooctyl di(isooctane)phosphonate, bis(2,2,4-trimethylpentyl) 2,2,4-trimethylpentanephosphonate, 2,2,4- trirnethylpentyl bis 2,2,4-trimethylpentane) phosphonate, bis(3,5,5 trimethylhexyl) 3,5,5, trimethylhexanephosphonate, bis(2-methyl-3-ethylpentyl) 2-ethyl-3-ethylpentanephosphonate, tetramethylbutyl bis(tetramethylbu tane)phosphonate, Z-methylheptyl bis(2-methylheptane)- phosphonate, bis(2,4,5,7-tetramethyloctyl) 2,4,5,7-tetramethyloctanephosphonate, 7,8-dimethyltetradecyl bis(7,8 dimethyltetradecane)phosphonate, bis(2,7-dimethyloctyl) 2,7-dimethyloctanephosphonate, 4-ethyll1eptyl bis(4-ethylheptane)'phosphonate and bis(2,6-dirnethylheptyl) 2,6- dimethylheptanephosphonate. A particularly desirable group of these compounds consists of alkyl esters of primary phosphonic acids in which each of the alkyl groups contains 8 to 10 carbon atoms.

The generic term phosphonic acids employed herein and in the claims includes both primary phosphonic acids (general formula: RP(O)(OH)2) and secondary phosphonic acids (general formula: R2P(O) (OH)), the Rs representing substituent groups linked to the phosphorus atom by direct carbon-to-phosphorus bonds. The term phosphonate is used to designate the esters of phosphonic acids. The term neutral ester is used to designate esters of phosphorus acids in which all of the acid groups are esterified. This terminology is in accord with that stated in Kosolapoff, Organo-Phosphorus Compounds, Wiley and Sons (1950), at page 4 thereof.

The compounds of the present invention can be prepared by the isomerization of neutral alkyl esters of phosphorous and phosphonous acids, in which esters the alkyl groups are branched-chain and contain at least 8 carbon atoms each, to form the corresponding esters of primary or secondary phosphonic acids. This isomerization can be effected by the use of catalytic amounts of a lower alkyl halide. In the reaction, the phosphorus shifts from the trivalent to the pentavalent state, the additional two valence bonds being occupied by an OX0 oxygen atom (=0).

The reaction may be illustrated generally by the following equations:

where R is defined as above, R is a lower alkyl group and X is a halogen atom.

This method of preparing the compounds of the inreactant involved. In preferred practice the reaction temperature is maintained within the range of from about 130 C. to about 190 C.

The reaction time should be suflicient to provide practical conversion to the desired product. The reaction time may be varied over the range of from about 1 to about 24 hours, as required, although in most instances a substantially shorter time, e. g., from about 1 to about 12 hours is entirely adequate.

The process may be carried out in a batchwise or a continuous manner, and at substantially atmospheric pressure, although superatmospheric pressure of from about 2 atmospheres to about atmospheres may be employed.

The novel compounds of the invention thus may be prepared conveniently in accordance with this process by reacting together a neutral, or full, ester of a phosphorous acid or a phosphonous acid and a lower alkyl halide. As the phosphorus ester there may be employed a triester of a phosphorous acid-a trialkyl phosphite-with the same branched-chain aliphatic alcohol, the alcohol containing more than 8 carbon atoms, and preferably from 8 to 10 carbon atoms. Suitable trialkyl phosphites which may be employed include, among others, tris(2-ethylhexyl) phosphite, tris(isooctyl) phosphite, tris(2,2,4-trimethylpentyl) phosphite, tris(tetramethylbutyl) phosphite, tris(Z-methylheptyl) phosphite, tris(2,4,5,7-tetramethyloctyl) phosphite, tris(7,8-dimethyltetradecyl) phosphite, tris(2,7-dimethyloctyl) phosphite and tris(4- ethylheptyl) phosphite. A particularly desirable group of these compounds comprises those compounds containing 8 to 9 carbon atoms.

Instead of a trialkyl phosphite, there may be suitably employed an alkyl diester of a phosphonous acid-a dialkyl alkanephosphonite-wherein the alkyl and alkane groups are the same, and each contains at least 8 carbon atoms and preferably from 8 to 10 carbon atoms. Suitable dialkyl alkanephosphonites include, among others, bis(3,5,5 trimethylhexyl) 3,5,5 trimethylhexanephosphonite, bis(2-ethylhexyl) Z-methylhexanephosphonite, bis(7,8-dimethyltetradecyl) 7,8-dimethyltetradecanephosphonite, bis(2-methyl-3-ethylpentyl) 2-methyl-3-ethylpentanephosphonite, bis(isooctyl) isooctane phosphonite, bis(2,5-dimethyloctyl) 2,7 dimethyloctanephosphonite and bis(2,4,5,7-tetramethyloctyl) 2,4,5,7-tetramethyloctanephosphonite. A particularly desirable group of these compounds is that in which the carbon chain contains 8 to 9 carbon atoms.

As the lower alkyl halide, there may be employed any monohalide of an alkane having not over 3 carbon atoms in the chain. Examples of this catalyst include, among others, methyl iodide and bromide, ethyl iodide and propyl bromide. In the preferred practice of the process, the alkyl halide is the monohalide of methane, and the most suitable member of this limited group has been found to be methyl iodide.

The isomerization of the neutral ester of a phosphorous or a phosphonous acid can be effected by heating the mixture of reactant and catalyst together at an elevated temperature. The lower alkyl halide is added to the phosphorus ester in an amount just sufiicient to cause the halide to act as a catalyst and not as a reactant. In general, the amount of lower alkyl halide added to the reaction mixture will constitute not over 10% (on a molar basis) of the amount of the phosphorus ester present, and the amount of the halide added preferably lies within the range of from about 2% to about 7% (on a molar basis) of the amount of the ester present in the reaction theatre.

The reaction temperature ordinarily lies within the range of from about 100 C. to about 250 C., the optimum temperature depending largely upon the particular The desired product may be obtained from the reaction mixture by (a) shaking the reaction mixture thoroughly with successive portions of 1 N sodium hydroxide solution until a separate caustic aqueous layer is obtained, followed by (b) thorough washing with successive portions of warm water until the organic reaction mixture is neutral, and (c) distillation of the mixture to remove the lower boiling components.

The following examples are presented for the purpose of illustrating the preparation of the compounds of the invention. It is to be understood that the invention is not intended to be restricted to the specific compounds stated and that other specific modifications are included by the invention. In the examples parts are parts by weight, unless otherwise indicated.

EXAMPLE I Bis(Z-ethylhexyl) Z-ethylhexanephosphonate was prepared by introducing 480 parts of tris(Z-ethylhexyl) phosphite and 10 parts of methyl iodide into a reaction vessel, and heating the mixture for 3 hours at 160 C. The amount of methyl iodide used represented 6% of the amount of the phosphite, calculated on a molar basis. Following the period of heating, the mixture was cooled, 300 ml. of 1 N sodium hydroxide solution was added, and the whole mixture agitated thoroughly. Then another 200 ml. of the caustic was added and the mixture agitated again. The organic liquid phase was allowed to separate from the aqueous liquid phase, and the latter removed. The organic liquid was then washed thoroughly with successive 50 ml. portions of warm water until the organic liquid was neutral. The organic liquid was then distilled, 286 parts of product being obtained. This represented a conversion of 59.5%. The product had an acid number of zero, a density (20/4) of 0.9098, a refractive index (20/d) of 1.4472 and a boiling point at 5 mm., mercury pressure, of 210 C. The per cent phosphorus calculated to be present was 7.41; the per cent phosphorus found to be present was 7.3. The prodnot had a viscosity at 100 F. of 8.71 centipoises, and at 200 F. a viscosity of 2.3 centipoises. The viscosity index is 79.

EXAMPLE II Di(isooctyl) isooctane phosphonate was prepared from tri(isooctyl) phophite. 327 parts of tri(isooctyl) phosphite and 7 parts of methyl iodide were heated together in a reaction vessel at a temperature of -170 C. for 9 hours. The amount of halide was equal to 0.65% (on a molar basis) of the phosphite. The mixture was then treated for separation of the product by the method stated in Example I. 205 parts of product were obtained, representing a conversion of 62.6%. The product had an acid number of 0.02, a density (20/4) of 0.9116, a refractive index (ZO/d) of 1.4471. The per cent phosphorus calculated to be present was 7.41; the per cent phosphorus found to be present was 7.6. The product had a viscosity at 100 F. of 11.26 centipoises and a viscosity at 200 F. of 2.76 centipoises. The viscosity index was 93.

EXAMPLE III ular interest for use as hydraulic fluids or as components of hydraulic fluids, and as lubricants for turbo-prop propulsion systems. Because of their stability and their compatibility with a wide range of other compounds, the

Preparation of bis(3,5,5-trimethylhexyl) 3,5,5-tri- 1 d b d l f th methylhexanephosphonate. Mix 460 parts of tris(3,5,5- 5 nave i g i euse 9 p as.lclzers or Syn trimethylhexyD phosphite and 7 parts of methyl bromide as We as Or.natura y occumng resms in a reaction vessel and heated at for The following data demonstrate the superiority of the hours. Cool the reaction mixture and separate the product compounfis of Invention over compounds dlsclosefi by the method Stated in Example L The product is by the prior art which are taught to be valuable as synthetic tained in substantial yield. 10 lutglcantsd I d H d d 1 d th ompoun s an are compoun s we ose 1n e EXAMPLE Iv prior art; Compounds III and IV are exemplary of the 3,5 ,5 -trimethylhexyl bis(3,5,5-trimethylhexane)phoscompounds of the invention.

Table I (B) Viscosity Index Small-Scale Oxidation-Corrosion (E) 0 a F 1 1901 1 1; (0) D W htL m ompoun or ua N90 oi n (DZ-ID) erg oss (mg /em $19M Cu Mg Fe ca Al Compound I-Dibuty1 n-octane-phosphonate (C4H9O)z(GaH 7)PO 0. 02 (-65 85 155 24.2 2.32 0 6.16 0 46.2 Compound II-Dibuty1 hexadecane-phosphonate (G4H90)1(C1UHN)PO 0.03 +45 149 149 20.7 0.08 0.28 0.24 0. 04 5.3 Compound IIIBis(2-ethy1hexy1) 2-ethy1- hexanephosphonate (OaHr10)2(CsH11)PO 0.00 -95 79 127 1.12 0.32 0.44 0.64 0.16 0.1 Compound IV-Di (isooetyl) isooctanennnsnhnnate (CaH 7O)2(CsH17)PO 0.02 90 93 126 0.84 0.16 0.00 0.12 0.00 0.31

phonate is prepared by following the procedure of Ex- We claim as our invention: ample III, with the single exception that 444 parts of bis- 1. A phosphorus ester having the formula (3,5,5-trimethylhexyl) 3,5,5-trimethylhexanephosphonite is substituted for the phosphite reactant.

EXAMPLE v 0=P(oR 368 parts of bis(7,8-d1methyltetradecyl) 7,8-d1methyltetradecanephosphonite are isomerized to 7,8-dimethyltetradeoyl bis(7,8-dirnethyltetradecane)phosphonate by where all the groups designated by the symbol R" are heating with 6 parts of methyl iodide at 170 C. until the identical in structure, and are branched-chain alkyl isomerization is complete. The product is separated from p each group Containing at least 8 Carbon atoms. the the reaction mixture by the procedure stated in Example I. symbol represents an integer selected from the group The compounds of the invention may also be illustrated of numbers conslstlllg 0f 1 and and the ym l 1 by the following examples: represents an integer equal to 3 minus m.

a Bis(2-methy1-3-ethylpenty]) 2-methyL-3-ethy1pen- 2. A b1s(d1alky1)alkane phosphonate 111 Which the alkyl lanephosphonate h h Structural formula; and alkanes groups are the same, and each consists of a branched-chain alkyl group containing at least 8 carbon H atoms. (CBHWCHWHI) OHOHHEIO-CHTCE(ofiflcmoflmhll 3. A bis( dia1kane)alkyl phosphonate in which the alkyl b. Z-ethylhexyl bis(2-ethylhexane)phosphonate: and alkane groups are the same, and each consists of a branched-chain alkyl group containing at least 8 carbon c. Tetramethylbutyl bis(tetramethylbutane)phosphonate:

atoms.

4. Bis(3,5,5-trimethy1hexyl)3,5,5-trimethy1hexanephosphonate.

5. Bis(2-ethy1hexyl)Z-ethylhexanephosphonate.

d. Bis(2,4,5,7-tetramethylocty1) 2,4,5,7-tetramethyloctanephosphonate:

6. Bis(isooctyl)isooctane phosphor-late. 7. 2-ethy1hexyl bis(2-ethylhexane)phosphonate.

e. Bis(4-ethylheptyl) 4-ethylheptanephosphonate:

Example VI The novel compounds of the invention, because of their stability and rheologicial properties, are of partic- Kosolapoif: Iour. Amer. Chem. Soc., V. 67, pages 1180-2 (1945).

Claims

1. A PHOSPHORUS ESTER HAVING THE FORMULA