US3681482A

US3681482A - Color improvement of phosphate esters

Info

Publication number: US3681482A
Application number: US8689A
Authority: US
Inventors: Vithal C Patel; Edward F Orwoll
Original assignee: FMC Corp
Current assignee: FMC Corp
Priority date: 1970-02-04
Filing date: 1970-02-04
Publication date: 1972-08-01
Anticipated expiration: 1989-08-01

Abstract

A process for the permanent removal of color from phosphate esters of alkylphenols which either are colored or become colored on storage by simultaneously bleaching and color-stabilizing the phosphate esters with sodium borohydride or lithium borohydride.

Description

ilnite fittes Patent Patelet al.

[ 51 Aug..1,1972

[54] COLOR IRQVENT 0F FHOSPTE ESTERS [72] Inventors: Vitlml C. Patel, Glen Burnie; Ed-

ward F. Orwoll, Baltimore, both of [73] Assignee: FMC Corpus-alien, New York, NY.

{22] Filed: Feb. 4, 1970 [21] Appl. No.: 8,689

[52] US. Cl. ..260/989, 260/966, 260/990 [51] Int. Cl. ..C07E 9/08, C07f 9/12 [58] Field of Search ..260/989, 990, 966, 967

[56] References Cited UNITED STATES PATENTS 3,356,775 12/1967 Mitchell ..2 60/990 3,1'50151 9/1964 Oldenburg ..260/621 A 3,202,719 8/1965 Jones ..260/966X Primary Examiner-Joseph Rebold Assistant Examiner-Richard L. Raymond Attorney-Eugene G. Seems, Charles C. Fellows and Pauline Newman 5 7] ABSTRACT 6 Claims, No Drawings COLOR IMPROVEMENT OF PHOSPHATE ESTERS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the preparation of low-color and color-stable alkylphenol esters of phosphoric acid.

2. Description of the Prior Art The production of low-color and color-stable phosphate esters made from alkylphenols has long been recognized to be a problem. Moreover, it has been noted that as the alkyl substitution of the aryl ring increases in going from tricresyl phosphate, i.e., tris(methylphenyl) phosphate, to compositions with increasing alkyl substitution, for example, tris(dimethylphenyl) phosphate, color increases. For example, tricresyl phosphate is sold as a commercial plasticizer typically having an acceptable platinumcobalt color of 75, as determined according to ASTM D-1209-2. Another triaryl phosphate ester, that is made from mixed cresols and xylenols and having about equal numbers of cresol and xylenol aryl groups, has a maximum platinum-cobalt color of 100. A triaryl phosphate made from a mixture of 2 k of xylenol to each half part of cresol, which is commercially available, typically has a platinum-cobalt colorof 200 and the so-called trixylyl phosphate has a platinum-cobalt color of 250.

A number of patents have issued on various methods for producing low-color, color-stable phosphate esters made from alkylphenols. Scott, in U.S. Pat. No. 1,958,210, issued May 8, 1934, discloses the use of decolorizing carbon for reducing the color of phosphate esters. Shuman in U.S. Pat. No. 2,113,951, issued Apr. 12, 1938, discloses a method for making color-stable phosphate esters by a route which involves distilling a phenol in the presence of a mineral acid such as sulfuric acid, hydrochloric acid, phosphoric acid, etc. to purify it, and employing the purified phenol to make tricresyl phosphate esters which are more stable to the action of heat and sunlight than esters made from phenols distilled in the absence of an inorganic acid.

A method of phenol color reduction is disclosed by Oldenburg in U.S. Pat. No. 3,150,191 to overcome a particular color problem in the case of phenols produced by the so-called cumene process. Cumeneprocess phenols, when chlorinated, produce undesirable color formation. However, by contacting the phenols with borohydride ions prior to chlorinating, chlorophenols of low color are produced.

Recently, a shortage of cresols and other suitable feed stocks for use in producing triaryl phosphate esters has made it desirable to make synthetic alkylphenols. Typical synthetic alkylphenols are mixed isopropylphenols. These mixed isopropylphenols have a good color, and when they are reacted with phosphorus oxychloride to make the corresponding phosphate ester, the ester itself can be made with good initial color, although frequently the ester has a platinum-cobalt color of 300-500. Surprisingly, although even when they have a good initial color, phosphate esters made from mixed isopropylphenols when stored in the dark change from a platinum-cobalt color of about 50-60 to a lemon yellow color of 300 to 500.

A process for decolorizing and color-stabilizing phosphate esters made from alkylphenols, and particularly isopropylphenols, against color formation is a principal object of this invention.

SUMMARY OF THE INVENTION We have now discovered a process for the permanent removal of color from tri(alkylphenyl) phosphate esters having excessive yellow color by bleaching the phosphate esters with 0.002 to 0.05 percent by weight of an alkali metal borohydride selected from the group consisting of sodium borohydride and lithium borohydride. The selected borohydride may be added either as a solid, or as a liquid solution of 0.01 to 10 percent by weight concentration. When phosphate esters are bleached by being contacted with 0.002 to 0.05 percent by weight based on the weight of the phosphate ester of a borohydride selected from the group consisting of sodium borohydride and lithium borohydride, and the resulting mixture is stirred from 5 to 24 hours, the phosphate ester not only is bleached, but surprisingly is stabilized against subsequent color formation.

DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS Alkylphenyl phosphate esters are typically made by reacting a cresol or alkylated phenol and phosphorus oxychloride at a molar ration of 3:1 in a reaction vessel equipped with a reflux condenser, by raising the temperature to about 180 C. or higher until the evolution of hydrogen chloride gas ceases. The resulting crude triaryl phosphate is distilled under vacuum and washed with a dilute alkali solution having a concentration of about 2 percent to remove free acids and unreacted alkylphenols. The product is frequently further processed to remove traces of color or odor by washing with water-soluble permanganate solutions or by treating with decolorizing agents such as activated carbon.

Permanent removal of color from discolored alkylphenyl esters according to the method of this invention is achieved by treating the phosphate ester with sodium borohydride or lithium borohydride. The preferred borohydride is sodium borohydride because it is the least costly of the borohydride materials commercially available. Sodium borohydride and lithium borohydride are used in effective amounts of 0.002 to 0.05 percent by weight based on the weight of the phosphate ester being bleached and stabilized. Levels higher than 0.05 percent may be used but have no added advantage and are uneconomical. The preferred amount is about 0.01 to 0.02 percent by weight. Surprisingly, the closely related potassium borohydride is not very effective as a bleaching and color-stabilizing agent for tri( alkylphenyl) phosphate esters.

We bleach and color-stabilize tri(alkylphenyl) phosphates by stirring them together with solid borohydride for from 5 minutes to 24 hours. Generally, the ester is treated for about 5 minutes to 1 hour at a temperature of about 20 to C., although preferably the treatment is carried out at about 45 to 55 C. The hot treatment can be followed by up to 24 hours stirring at ambient temperature. A moderate temperature of about 50 C. is preferred as the higher temperatures tend to decompose the sodium borohydride without properly bleaching the phosphate ester. The bleach can be carried out at higher than atmospheric pressure, although atmospheric pressure is preferred as a matter of convenience. The phosphate ester may be diluted with an inert organic solvent and the borohydride can be used in solution in a solvent if desired, although it is preferred not to use any kind of a solvent or diluent for either the phosphate ester or the borohydride.

The phosphate ester can be treated with solid borohydride or an aqueous solution of borohydride. The solid treatment is preferable because of the ease of work-up after the treatment. The borohydride treatment of a phosphate ester can be carried out batchwise or in a continuous manner.

The borohydride treatment should be done under neutral or alkaline conditions, as strongly acidic conditions decompose sodium borohydride instantly. The presence of moisture in the phosphate ester does not adversely affect the bleaching properties of sodium or lithium borohydride.

The effective concentration of sodium or lithium borohydride depends on the history of the phosphate ester. Excessive exposure of tri( alkylphenyl) phosphate esters to air during purification causes a build-up of color which is difficult to remove, and as much as 0.05 percent sodium borohydride may be required to bleach the ester and stabilize it against subsequent color formation. Phosphate esters made under normal processing conditions generally require 0.01 percent or less by weight of solid sodium borohydride to effect adequate bleaching and to stabilize the ester against subsequent color formation. The time required to bleach a phosphate ester also depends upon its history during its production. Phosphate esters which have undergone excessive exposure to air during purification develop a stubborn color that resists bleaching, and as long as 24 hours may be required to obtain an adequate bleach. However, in most cases involving tri(alkylphenyl) phosphate esters produced under normal operating conditions, it generally takes about 1 hour with a 0.01 percent sodium borohydride concentration to effect bleaching and color stabilization.

The rate of bleaching, aS well as the rate of decomposition of the borohydride, increases as the temperature increases. The bleach can be conducted at temperatures between 20 and about 100 C. However, practice has taught that about 50 C. is a good choice of an average temperature at which to bleach the phosphate esters. Good agitation, suflicient to keep the borohydride uniformly suspended in the phosphate ester during bleaching, is necessary. At the end of the bleaching period, the unreacted borohydride and byproducts are filtered from the phosphate esters by ordinary filtration procedures.

The following examples, illustrating the novel method disclosed herein, are given without any intention that the invention be limited thereto. All parts and percentages are by weight, unless otherwise noted.

EXAMPLE 1 A 500 gram sample of a tri(alkylphenyl) phosphate with a platinum-cobalt color of 200, determined according to ASTM D-1209 Standard Method Test for Color of Clear Liquids (platinum-cobalt scale), made from mixed isopropylphenols composed of a mixture of monoisopropylphenols, diisopropylphenols, triisopropylphenols and some unsubstituted phenol, was washed with a 2 percent by weight solution of sodium hydroxide in water and then treated with carbon at 120 C. To the dried phosphate ester was added 0.05 grams of sodium borohydride, and the mixture was stirred in the dark at 50 C. for 30 minutes, after which the mixture was filtered warm to remove the unreacted sodium borohydride and solid by-products. The treated ester had a platinum-cobalt color rating of 25. Samples of the untreated and bleached product were stored in the dark for 12 months during which the untreated sample had turned yellow while the color of the treated sample remained unchanged at about 25 platinumcobalt color.

EXAMPLE 2 Example 1 was repeated using 0.1 grams of sodium borohydride to treat 500 grams of the tri(alkylphenyl) phosphate. The color of the product was reduced to a platinum-cobalt color of 20.

EXAMPLE 3 A 500 gram sample of tri(propylphenyl) phosphate was treated as described in Example I with 0.05 grams of sodium borohydride and the platinum-cobalt color of the phosphate was reduced from to 10.

EXAMPLE 4 Example 1 was repeated using only 0.025 grams of sodium borohydride to treat 500 grams of the tri(alkylphenyl) phosphate. The platinum-cobalt color of the tri(alkylphenyl) phosphate was reduced from 300 to 40.

EXAMPLE 5 To 27.5 pounds of tri(propylphenyl) phosphate was added 0.00275 pounds (0.01 percent) of sodium borohydride and the resulting mixture was stirred in the dark at 50 C. for 1 hour. The mixture was filtered warm. The platinum-cobalt color of the tri(propylphenyl) phosphate was reduced from 300 to 15.

EXAMPLE 6 Example 1 was repeated using a tri(alkylphenyl) phosphate with an initial platinum-cobalt color of 100. After addition of the sodium borohydride, the temperature of the phosphate-borohydride was raised to 75 C. and the temperature of the mixture was maintained at 75 C. for 15 minutes. The tri(alkyl-phenyl) phosphate, after treatment, had a platinum-cobalt color of 25.

EXAMPLE 7 Example 6, was repeated except that the phosphate ester was preheated to 75 C., sodium borohydride was added, and the mixture was maintained at 75 C. for 15 minutes. The platinum-cobalt color of the phosphate ester was reduced from to 50.

EXAMPLE 8 Example 7, was repeated using a treating temperature of 100 C. and 0.02 gram of sodium borohydride was used. The platinum-cobalt color of the phosphate ester was reduced from 100 to 60.

EXAMPLE 9 A 100 gram sample of the tri(alkylphenyl) phosphate of Example 1 was washed with a 2 percent by weight solution of sodium hydroxide in water and the washed sample was then treated with 0.5 parts by weight of activated carbon at 120 C. and filtered. The filtered phosphate was treated with 10 grams of a 0.1 percent 1 by weight solution of sodium borohydride in water, and the aqueous layer which formed was separated from the phosphate ester by decantation. The treated ester was then dried by heating at ll0-l30 C. for minutes under nitrogen. The platinum-cobalt color of the phosphate ester was reduced from 300 to 20.

EXAMPLE 10 A 200 gram sample of the tri( propylphenyl) phosphate was mixed with 0.02 gram of lithium borohydride and stirred in the dark while the temperature was being raised to 50 C. In less than 8 minutes after adding the lithium borohydride and before the temperature reached 50 C., the color essentially disappeared. The mixture was filtered warm. The platinumcobalt color of the phosphate ester was reduced from 400 to 10 by the treatment.

COMPARISON EXAMPLE A To a 200 gram sample of the phosphate ester of Example 10 was added 0.10 gram of potassium borohydride. The mixture was stirred in the dark at 50 C. for 4 hours with a very slight reduction in platinumcobalt color of 400 to about 370. No more reduction in color was observed, even after 24 hours treatment at room temperature. This example was repeated using an aqueous solution of the potassium borohydride and again there was practically no reduction in color.

COMPARISON EXAMPLE B Tris(isopropylphenyl) Phosphate Made from lsopropylphenols Bleached with Sodium Borohydride A mixture of 650 grams of synthetic isopropylphenols, as described in Example 1, but darker in color (Gardner scale color-9)*, 325 grams of distilled water, and 1.95 grams of sodium borohydride was stirred at 50 C. for 2 hours. The resulting mixture was distilled at atmospheric pressure to obtain 602 grams of practically water-white (platinum-cobalt color- 10) isopropylphenols.

A one-liter, three-neck round-bottom flask,

equipped with condenser, thermometer, stirrer and addition funnel, was charged with 600 grams of distilled isopropylphenols (4.61 moles of mixed phenols) and 3.0 grams (0.025 mole) of aluminum chloride catalyst. To the reaction mixture, at 1l5l20 C., was added 196 grams 1.28 mole) of phosphorus oxychloride over a 2-hour period. The resulting mixture was stirred at 0 180 C. for 3 hours. It was then allowed to cool to about This invention has been explained and exemplified in I a manner so that it can be readily practiced by those skilled in the art. The best mode contemplated by the inventor has been set forth. Clearly, within the scope of the appended claims, the invention can be practiced by those skilled in the art having the benefit of the disclosure, otherwise than as specifically described and exemplified herein.

What is claimed is:

1. A process for bleaching and color-stabilizing a tri(alkylphenyl) phosphate ester comprising bleaching the ester with from 0.002 percent to 0.05 percent by weight based on the phosphate ester of an alkali metal borohydride selected from the group consisting of sodium borohydride and lithium borohydride by mixing the borohydride together with the ester at a temperature between 20 and C. for a period of from 5 minutes to 24 hours.

' 2. The process of claim 1 in which the alkali metal borohydride is sodium borohydride.

3. The process of claim 1 in which the alkali metal borohydride is lithium borohydride.

4. The process of claim 1 in which the temperature is between 45 and 55 C.

5. The process of claim 1 in which the processing period is between 15 minutes and 1 hour.

6. The process of claim 1 in which the alkali metal borohydride is present in an amount of 0.01 to 0.02 percent by weight based on the phosphate ester.

UNTTED STATES PATENT @FFTCE QERTTTTQATE CT CCRREQTTCN Patent No. 2 68 1 L[82 Dated August 1, 1972 Inventor(s) Vithal C. Patel and Eward F. Orwoll It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 20, "2" should read---6 2--.

Column 2, line 30, "ration" should read --ratio--,.

Column 3, line U6, "aS" should read -as-.

Column l, line 55, "tri(alkylphenyl) should read tri(alkylphenyl)-.

Column 5, line &6, The following footnote relating to the asterisk was omitted:

*Gardner scale color, determined according to ASTM D-l5 4 l-68 7 Standard Test for Color of Transparent Liquids (Gardner Scale) is used to describe the color of liquids that are transparent but relatively dark; the platinum-cobalt color scale is used to describe liquidsthat are very light in color, that is, close to "water-White" I Signed and sealed this 25th day of December 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. D. TEGTMETZER f Attesting Officer Acting Commissioner of l atents ORM PC4050 (10-69)

Claims

2. The process of claim 1 in which the alkali metal borohydride is sodium borohydride.
3. The process of claim 1 in which the alkali metal borohydride is lithium borohydride.
4. The process of claim 1 in which the temperature is between 45* and 55* C.
5. The process of claim 1 in which the processing period is between 15 minutes and 1 hour.
6. The process of claim 1 in which the alkali metal borohydride is present in an amount of 0.01 to 0.02 percent by weight based on the phosphate ester.