WO1984004923A1

WO1984004923A1 - Liquefied mixtures of trialkylphosphine oxides

Info

Publication number: WO1984004923A1
Application number: PCT/US1984/000804
Authority: WO
Inventors: Richard Williamson Cummins; Burton Murry Baum
Original assignee: Fmc Corp
Priority date: 1983-06-13
Filing date: 1984-05-24
Publication date: 1984-12-20
Also published as: EP0144423A1

Abstract

Liquefied mixed trialkylphosphine oxides useful in formulating low density hydraulic fluids.

Description

LIQUEFIED MIXTURES OF TRIALKYLPHOSPHINE OXIDES

This invention relates to phosphine oxides, and in particular to liquefied mixtures of tr ialkylphosphine oxides useful as components in aircraft hydraulic fluids and in other formulations.

Modern aircraft are equipped with a number of hydraulically actuated mechanisms such as brakes, power steering for taxiing, landing gear, control surfaces, that is, wing flaps, elevator, rudder and the like. In a large wide-bodied airliner, the quantity of hydraulic fluid that must be carried can be substantial upwards of about 175 gallons. The substitution of a hydraulic fluid with a specific gravity of 0.878 instead of 1.00 amounts to a weight savings of about 200 pounds over the commonly used phosphate ester based hydraulic fluids. A comparable product having a lower specific gravity would be of benefit to the aircraft industry.

It has now been discovered that liquid mixed trialkylphosphine oxides are excellent base stocks in the formulation of low density hydraulic fluids and the provision of such compositions and their use in hydraulic devices and processes constitutes the principal objects and purposes of the invention.

The herein liquefied trialkylphosphine oxides are obtained by combining individual members to provide mixtures which through mutual melting point depression remain in the liquid state. Generally speaking, trialkylphosphine oxides, as single compounds, are highly crystalline solids. Although they constitute a known chemical series, trialkylphosphine oxides have not, so far as can be ascertained, been prepared and utilized as liquefied mixtures.

In forming the liquefied trialkylphosphine oxide mixtures of the invention, the maximum number of individual members should be used to insure that crystallization does not occur. Thus, trialkylphosphine oxides can be selected in which the alkyls are alike or dif ferent with respect to their isomeric configuration and number of carbon atoms. For instance, a mixture of trialkylphosphine oxides in which the number of carbon atoms per alkyl is 6 to 10 would include a large number of homologous and isomeric compounds. However, the synthesis of sufficient numbers of different structures in order to provide and maintain stable liquefied mixtures can be arduous and time-consuming. It has been found that this laborious procedure can be circumvented and entirely satisfactory liquefied trialkylphosphine oxides obtained by phosphinating mixtures of α-olefins followed by oxidation of the trialkylphosphine mixture. The reaction is carried out in the presence of a free radical initiator as illustrated in the following scheme:

3RCH=CH₂ + PH₃ Azobisisobutyronitrile

P(CH₂CH₂R)₃ + [O] (CH₂CH₂R)₃

wherein R is alkyl in an olefinic mixture. From the standpoint of economy and convenience, RCH=CH₂ is preferably an even numbered olefin since these are readily available as by-products from petroleum refineries. Typically, the reaction sequence is conducted by introducing phosphine into a molar excess of the monoolefin mixture in the presence of the radical initiator under inert conditions at moderately elevated temperatures about 80°C to about 120°C. The resulting intermediate phosphines are then oxidized, preferably with hydrogen peroxide, to the corresponding mixed phosphine oxide. Suitable radical initiators include any number of compounds which are photochemically or thermochemically decomposed to form free radicals under the reactive conditions. A preferred radical initiator is azobisisobutyronitrile. Generally speaking, the reaction was carried out following the procedure for preparing individual trialkylphosphine oxides as set forth in U. S. Patent No. 2,803,597 to Stiles and J. Org. Chem. 26, 5138 (1961).

The reaction of phosphine with α-olefinic mixtures in molar ratios of 1:1:1 results in a statistical distribution of phosphine oxides, although variations in the reactivities of the individual olefins in the mixture may alter the distribution to some extent. By varying the olefinic molar ratio, however, relatively large shifts in the distribution of products can be realized. For instance, it may be desirable to include a preponderance of a higher molecular weight olefin in the mixture in order to suppress the vapor pressure of the liquefied trialkylphosphine oxides to permit their use at elevated temperature. In Table 1 is listed the properties of various trialkylphosphine oxides. The hydraulic fluids of the invention will normally contain very minor amounts, typically about 0.01% to about 5.0% by weight of various additives of the type normally incorporated in formulating hydraulic fluid compositions such as antioxidants, rust inhibitors, corrosion inhibitors, antifoam agents, antiwear agents, cavitation inhibitors, pour point depressants, and other special purpose additives.

Rust and corrosion inhibitors commonly employed include benzothiazole, benzotr iazole, tr iethanolamine, phenothiazine, trialkyl phosphites, N-acrylsarcosines, propyl gallate, succinic acid and alkylsuccinic acids. Additives to inhibit foaming and cavitation include organosilicones, dialkyl carboxylic acid esters such as diethyl succinate or dioctyl sebacate. Antioxidants include dialkylthiodipropionate, for example, dilaurylthiodipropionate, etc., organic amines, for example, diphenylamine, phenylnaphthylamine, hindered phenols, etc.

As previously pointed out, the herein trialkylphosphine oxides are characterized by exceptionally low density and are thus particularly suitable as the base stock in hydraulic fluids for aircraft. Whereas, the common commercial phosphate ester type hydraulic fluids, for example, tributylphosphate and dibutylphenylphosphate have a specific gravity of about at least 1.000, the trialkylphosphine oxides of the invention exhibit an average specific gravity of about 0.878. This translates into substantial weight savings for large commercial airliners such as the 747 which has a hydraulic fluid capacity of about 175 gallons. Furthermore, the herein liquefied mixtures of trialkylphosphine oxides have one-thousand-fold lower volume resistivities than phosphate esters which should decrease flow of wall currents induced by the high velocity flow through control valves thereby inhibiting erosion of hydraulic systems. The invention is further illustrated by the following example:

Tri(C₆-C₈-C₁₀) Phosphine Oxide Example 1 To a 1-liter 316 SS stirred autoclave evacuated to 10 mm Hg pressure was added 135.0 g (1.61 moles) of hexene-1, 188.0 g (1.68 moles) of octene-1, 241.0 g

(1.72 moles) of decene-1, and 0.4 g of azobis isobutyronitr ile. Phosphine (51.0 g, 1.50 moles) was then added and the reaction mixture heated with agitation to 85°C- 90°C and held at this temperature for a total of 10 hours. A toluene solution of azobis isobutyronitr ile, made by dissolving 1.6 g of azobis isobutyronitr ile in 50 g of toluene, was added in two equal portions after the first and second hours of reaction time.

At the end of the 10 hour reaction period, the reaction mixture was vacuum stripped at 100°C and 30-50 mm Hg (4 to 6.7 kPa) to remove toluene and unreacted olefins and the residue taken up in 600 ml of isopropyl alcohol and oxidized by the dropwise addition of 122 ml of 30% hydrogen peroxide (1.08 moles). The oxidized mixture was vacuum stripped at 30°C and 5 mm Hg (667 Pa) to give 559 g of crude tri(C₆-C₈-C₁₀) phosphine oxide corresponding to 96.5% of theory based on phosphine. The crude product, having an acid number of > 4, was dissolved in 300 ml of petroleum ether and stirred for 3 hours with 250 ml of saturated aqueous Na₂CO₃ solution and 100 ml of saturated aqueous NaCl solution. After phase separation and vacuum stripping at 30°C and

5 mm Hg (667 Pa), 378.5 g of liquid product was obtained corresponding to a 65% yield of tri(C₆-C₈-C₁₀) phosphine oxide (C₆/C₈/C₁₀ = 1.0) based on phosphine. Found: C, 73.93; H, 13.01; P, 8.19. Calculated for C₂₄H₅₁OP: C, 74.61; H, 13.21; P, 8.03. Acid number was 0.5. Product was oil-soluble and water-insoluble. Viscosity index was 77. Pour point was +17°F. Specific gravity at 20/20°C was 0.878. Volume resistivity at 10 volts and 23°C was 10⁶ ohm-centimeter. In addition to their use in aircraft hydraulic systems, the herein liquefied trialkylphosphine oxide mixtures exhibit antistatic properties as evidenced by the marked decrease in volume resistivity of thermoplastic polymers in which such phosphine oxides have been incorporated. The liquefied trialkylphosphine oxide mixtures possess other useful and valuable characteristics. For instance, liquid decyl hexyl octylphosphine oxide, a representative member of the series obtained by reacting molar proportions of 1-hexene, 1-octene and 1-decene with phosphine followed by oxidation of the reaction mixture, is capable of plasticizing nylon. This is indeed surprising in view of nylon's inertness and incompatibility with the normally used plastic izers. Even more surprising, however, are the properties of nylon plasticized with the herein liquid trialkylphosphine oxides. Particularly noteworthy in this regard is the unusually high luster of fibers spun from these novel plasticized nylon compositions. Dyed fabrics manufactured from such transparent fibers should, therefore, exhibit much greater color brightness compared with conventional nylon textiles. Another surprising and further unexpected prop erty of the herein plasticized nylon is that during cold drawing, the resulting fibers become increasingly more extendable without any apparent loss of tensile strength. Normally, incorporation of plasticizer in a polymer causes a decrease - not an increase in physical strength.

Plastic films containing the liquid trialkylphosphine oxides of the invention are rendered more transparent. For example, polyethylene film, which tends to be milky or hazy, was obtained in highly clarified form. Similar results were realized with nylon film.

Claims

CLAIMS:

1. A liquid mixture of tr ialkylphosphine oxides produced by exhaustively alkylating phosphine (PH₃) with a mixture of α-olefins having a carbon content of 6 to 10 carbon atoms followed by oxidation of the resulting mixture of tr ialkylphosphines.

2. The composition of claim 1 characterized in that the α-olefins are a 1:1 :1 molar mixture of hexene-1, octene-1 and decene-1.