BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to the preparation of alkyl tetrabromophthalates produced by the reaction of tetra- bromophthalic anhydride with alkanols in the presence of titanium (IV) lower alkoxide catalyst.

Description of the Prior Art

The known synthesis of biε(2-ethyl-l-hexyl) tetrabromo¬ phthaiate involves the reaction of tetrabromophthalic anhydride with 2-ethyl-l-hexanol in the presence of titanium (IV) isopro¬ poxide as catalyst. However, the prior art processes for recov¬ ering the product have been unsatisfactory because of residual acidity in- the reaction product and the presence of insoluble titanium catalyst residue. For example, Spatz, et al., "Diβcol- oration of Tetrabromophthalic Anhydride Polyester Resins," I&EC Product Research and Development, Volume 8, December, 1969, pages 391, 395, describe two variations in the recovery of biε(2-ethyl- 1-hexyl) tetrabromophthaiate obtained by acid catalyzed

esterification of tetrabromophthalic anhydride. The authors first suggest using low pressure distillation to recover the product after an elaborate purification by washing. Alternatively, the use of column chromotography is described. However, neither technique appears to be totally effective or commercially practicable.

Japanese Patent 50/5701, issued March 6, 1975, de¬ scribes a product purification approach involving the removal of excess alcohol in vacuo, followed by treatment of the crude ester with activated clay. Again, the reported results did not yield levels of satisfactory product quality.

U.S. Patent 4,214,103 describes the purification of crude halogenated products, especially nuclear halogenated products produced by contacting an excess of bromine with the aromatic compound such as diphenyl ether in the presence of a bromination catalyst such as iron, aluminum and their halides. The described process comprises contacting the crude nuclear halogenated product with a finely divided basic solid such as a carbonate or bicarbonate of an alkali metal or ammonia in an organic solvent or in a molten state in the presence of a small amount of water. While the described process was successful in achieving its objectives, it did not deal with the problems posed by the recovery of biε(2-ethyl-l-hexyl) tetrabromophthaiate, that

is, the necessity of reducing residual acidity and removing titanium containing catalyst residue.

Accordingly, a primary object of the present invention is to provide a process for recovery of alkyl tetrabromophthal- ates.

A related object is to provide a method for recovery of bis(2-ethyl-l-hexyl) tetrabromophthaiate produced by the reac¬ tion of tetrabromophthalic anhydride and 2-ethyl-l-hexanol in the presence of titanium isopropoxide catalyst.

A still further object is to provide a method of recovering biε(2-ethyl-l-hexyl) tetrabromophthaiate which reduces residual acidity in the finished product to a very low level and which converts the titanium containing catalyst residue to a form that can be separated from the reaction product by filtration or other physical means.

SUMMARY OF THE INVENTION The foregoing and other objects, advantages and fea¬ tures of the present invention may be achieved with a method for recovering alkyl tetrabromophthaiate obtained by reacting tetra- bromophthalic anhydride with an alkanol in the preβence of titanium lower alkoxide catalyst. The method comprises the steps of contacting the reaction mixture with an effective amount of

sodium carbonate decahydrate with agitation for time and at a temperature sufficient to enhance the quality of the product; and isolating alkyl tetrabromophthaiate from the reaction mixture. Effectiveness of the product recovery techniques of this inven- tion are optimized by conducting the initial treatment with sodium carbonate in a closed system in the presence of a small but effective quantity of water supplied by the sodium carbonate decahydrate, with that water being removed before the product is isolated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The process of producing alkyl tetrabromophthaiate by reacting tetrabromophthalic anhydride with an alkanol in the presence of titanium lower alkoxide catalyst is well known in the art. The product produced by the foregoing reaction, however, generally exhibits an undesirably high level of acidity (e.g. _ 3 eq./lOO grams or more). Moreover, the titanium catalyst residue exists in a soluble form in the reaction mixture and is difficult to separate from the product.

In general, tetrabromophthalic anhydride is reacted with alkanol in the presence of titanium lower alkoxide catalyst in any suitable reaction vessel. The reaction preferably is conducted under a nitrogen atmosphere.

The alkanol reacted in accordance with this invention may be a C., _lβ alkanol, preferably a C ₄ _- _g alkanol. Especially

preferred alkanolε in accordance with this invention include 2-ethyl-l-hexanol and mixtures of C _g _ ₁₀ alcohols, especially mixtures of hexyl, octyl and decyl alcohols.

The titanium lower alkoxide catalyst may be a titanium C,_ ₄ alkoxide such as the ethoxide, propoxides, and butoxides of titanium (IV). Titanium isopropoxide is especially preferred.

Products prpduced by the foregoing reaction are C, - ₈ alkyl tetrabro ophthaiateε. Preferred products include C, -, alkyl tetrabromophthalates. Bis(2-ethyl-l-hexyl) tetrabromoph- thalate, obtained from the reaction of 2-ethyl-l-hexanol with tetrabromophthalic anhydride, is an especially preferred product in accordance with this invention. Mixture of hexyl, octyl, and decyl tetrabromophthalates are also preferred in accordance herewith. An exceεε of alkanol is desirably employed as is well known to thoεe εkilled in the art (e.g., about 5-100 percent, baaed on tetrabromophthalic anhydride). The amount of titanium lower alkoxide catalyst is also maintained within known limits (generally about 0.05-5.0 volume percent based on tetrabromoph- thalic anhydride). Preferably, about 50 percent excess alkanol and about 0.5 volume percent titanium lower alkoxide are employed.

It has been found that the desired recovery objectives may simply and easily be met by treating the crude alkyl tetra- bromophthaiate reaction mixture with crystalline sodium

carboπate decahydrate with agitation at elevated temperatures. Desirably, the initial stage of the recovery process is carried out in a closed system in the presence of a small but effective amount of water supplied by the water of hydration of sodium 5 carbonate decahydrate. The process of the present invention reduces the original acidity to a very low level and, additionally, causes precipitation of the titanium catalyst residue so that it can be separated by filtration during product isolation.

0 The crystalline sodium carbonate decahydrate may conveniently be added to the reaction mixture in the product reactor or other convenient vesεel following the conclusion of the eεterification reaction. Substantially any effective amount of sodium carbonate decahydrate may be added in order to achieve the benefitε of the present invention. Preferably about 0.1-20 percent sodium carbonate decahydrate, by weight of the reaction mixture, is employed. It iε especially preferred to employ about 5 weight percent sodium carbonate decahydrate by weight of the reaction mixture.

Alternatively, the sodium carbonate decahydrate may be ι supplied in the form of anhydrous sodium carbonate in combination- with that amount of water corresponding to the decahydrate (i.e.,. '10 moles of water per mole of anhydrous sodium carbonate). For:, example, about 1.7 liters water is added per kilogram of

anhydrous sodium carbonate utilized in accordance with this invention.

The reaction mixture containing the sodium carbonate decahydrate is agitated at elevated temperature. Desirably, the 5 reaction mixture is maintained at a temperature in the range of about 30-120°C. A temperature of about 90 ^β C is especially preferred.

The reaction mixture containing sodium carbonate is agitated at elevated temperature for a period of time sufficient 0 to effect the desired quality improvement. Desirably, the agitation continues for about 0.5-1 hours, although shorter or longer times may be employed as long as acidity is reduced to satisfactory levels and catalyst residues are separated from the product after the remaining water is removed.

5 Alkyl tetrabromophthaiate is then isolated from the mixture, which is filtered to separate catalyst residues and other undesirable materials.

One preferred method of product isolation involves passing a stream of air above the reaction mixture while subject- o ing it to additional heating to a temperature in the range of about 100-150°C, preferably about 130°C, for about 0.5-1 hours in order to remove the water provided by the sodium carbonate

decahydrate. After the water has been removed, the product can be cooled and filtered in order to separate catalyst residue and other impurities from the purified product, and stripped in order to remove the unreacted alcohol.

5 Alternatively, the product may also be isolated by passing steam through the liquid reaction mixture and collecting a two-layer distillate of aqueous and organic phases, followed by removal of the residual water by azeotropic distillation up to about 130°C. The product may again be further treated by filtra- 0 tion.

EXAMPLES Example jL Preparation of Bis 2-ethyl-l-hexyl) Tetrabromophthaiate Tetrabromophthalic anhydride (1391.1 grams; 3.0 moles),

2-ethyl-l-hexanol (1171.8 grams; 9.0 moles) and titanium (IV) isopropoxide (7 ml.; 0.5 volume percent on tetrabromophthalic anhydride) were charged into a 3,000 ml. reaction flask main¬ tained under a nitrogen atmosphere. The reaction flask was fitted with a mechanical stirrer, thermometer, nitrogen inlet tube, and a Dean-Stark water trap connected to a Friedrich condensor. The reaction mixture was heated with agitation at a 'temperature equal or less than about 200°C for eight hours. The

resulting product (2,497 grams) was an amber thick clear liquid having an acidity of 1.4 meq. per 100 grams.

Example 2. Recovery of Bis(2-ethyl-l-hexyl) Tetrabromophthaiate

The reaction mixture from Example 1 was cooled to approximately 90°C, and the Dean-Stark water trap was removed and replaced with a reflux condenser. Nitrogen flow was shut off, and sodium carbonate decahydrate crystal (124.9 grams. , 5 weight percent by weight on the reaction mixture) was added to the reaction mixture with efficient agitation at about 90°C for about 0.5 hours.

The bis(2-ethyl-l-hexyl) tetrabromophthaiate was isolated from the reaction mixture, which contained some unre- acted 2-ethyl-l-hexanol, by steam distillation of the alcohol, followed by nitrogen purge at 130°C and filtration of the purged residue at about 110-115°C.

Product yield from filtration was 2030.0 grams, about 95.9 percent based on the tetrabromophthalic anhydride starting material. Additional quantities of high quality bis(2- ethyl-1-hexyl) tetrabromophthaiate may be isolated from the spent sodium carbonate filtration residue and thus permitting a total

yield of 2105.6 grams, 99.4 percent based on the tetrabromoph¬ thalic anhydride starting material. Properties of the isolated bis(2-ethyl-l-hexyl) tetrabromophthaiate product are given in Table I.

⁵ TABLE I

Product Properties

Appearance: Gold, clear thick liquid

Br (calcd. 45.3%): 44.8%

Acidit : iO.Ol meq./lOO g. 0 Ash: 0.04%

VPC Assay: 2-ethyl-1-hexano1: 0.43 area %

Tetrabromo¬ 0.04 area % phthalic anhydride Bis(2-ethyl-l-hexyl)- 92.9 tetrabromo phthalate

Example 3. Comparative Example A series of recovery runs were conducted in order to evaluate the efficacy of a variety of purification agents. The agents were either uβed "neat,** that is, the agents were added to the crude bis(2-ethyl-l-hexyl) tetrabromophthaiate reaction mixture, or they were added to the crude product provided in an organic solvent (methylene chloride or toluene) . The bis<2- -

ethyl-1-hexyl) tetrabromophthaiate product was recovered from the treated mixture by filtration and/or by stripping. The results given in Table II.

TABLE II Purification Agent Acidity (meg/100 σ. )

None 2.65 a ₂ C0 ₃ .H ₂ 0 ≤O.OOl a^COg.H _j O (open/closed) 0.774 ₂ CO ₃ .10H ₂ O (closed/open) ≤O.OOl ^Na 2 ^C0 3 ¹ * ⁵³

CaO 0.23

CaC0 ₃ 2.70

Propylene Oxide 0.44

NH ₄ 0H 2.08 H ₂ H ₂ .H ₂ 0 0.27

H ₂ 0 ₂ 2.79

Activated Carbon 2.29

Tonsil Clay 2.64

Attapulguε Clay 2. 5 NH ₃ (gaε) 0.98

C0 ₂ 2.57

Std. Waεhing 0.014 a ₂ C0 ₃ in Toluene 0.56 a ₂ C0 ₃ .H ₂ 0 in Toluene 1.16 a ₂ C0 ₃ .10H ₂ 0 in Toluene ≤0.005

The data in Table II demonεtrate that use of an orga solvent to aid in recovery is not advantageous. In addition, all. of the agents tested, only sodium carbonate decahydrate an sodium carbonate monohydrate produced a product with the desir low level of acidity. In addition, sodium carbonate decahydra is significantly more effective than sodium carbonate monohydr because the reaction mixture filters faster when the decahydra is used.

Thus, recovery of bis(2-ethyl-l-hexyl) tetrabromopht late using the process of the present invention is the only approach that permits the desired level of neutralization of residual acidity to be achieved, that converts the titanium catalyst residue from soluble to insoluble form which may be removed by filtration, and that results in easy and fast filtr tion.