Production of phthalic esters

In Western Europe and Japan, over 60% of the phthalic anhydride is used in the production of phthalic esters in the United States this figure is around 55%. 

Other applications for phthalic anhydride are the production of alkyd resins and unsaturated polyester resins, each representing around 20%, complemented by the production of dyes and pigments. 

The main application for phthalic anhydride is the production of phthalic esters for use as plasticizers. 

Plasticizers are auxiliary agents used in the industrial processing of plastics. By lowering the intermolecular forces between the molecular chains, they endow high polymeric substances with certain desirable physical characteristics, e.g. reduced brittleness, higher plasticity, increased elastic properties, lower hardness and, where necessary, increased adhesion. 

James A. Cutting was the first to discover, in 1854, that camphor was a suitable plasticizer for nitrocellulose. 

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Today, glycerol has over 2000 different applications, in cosmetics, pharmaceutics, foods and drinks, tobacco, paper, inks and printing colors, the production of phthalic and maleic alkyd resins and crosslinked polyesters, and as a hydraulic agent. Polyglycerols have a wide range of applications as emulsifiers, and technical esters of glycerol with fatty acids are used as synthetic lubricants [4]. 

Phthalic anhydride Decomposition product of phthalate esters or resins paint off-gas product... 

The PhEur 2005 and USPNF 23 describe cellulose acetate phthalate as a reaction product of phthalic anhydride and a partial acetate ester of cellulose containing 21.5-26.0% of acetyl (C2H3O) groups, and 30.0-36.0% of phthalyl(o-carboxybenzoyl, CgHjOs) groups. 

Production and uses of xylene derivatives 273 Table 7.2 Characteristic properties of phthalic esters... 

Phthalic anhydride (phthalic-acid anhydride) n. C6H4(C0)20. a white, odorless, crystalline compound derived by oxidation of naphthalene or o-xylene, shipped in flake or molten form. It major use is in the production of phthalate esters for plasticizing vinyl and cellulosic resins. It is also an important intermediate in the manufacture of alkyd and unsaturated polyester resins, and is a curing agent for epoxy resins. Bp, 284°C mp, 130°C Sp gr, 1.53 acid value, 758.0 See image). 

Reactions of the Methyl Groups. These reactions include oxidation, polycondensation, and ammoxidation. PX can be oxidized to both terephthahc acid and dimethyl terephthalate, which ate then condensed with ethylene glycol to form polyesters. Oxidation of OX yields phthaUc anhydride, which is used in the production of esters. These ate used as plasticizers for synthetic polymers. MX is oxidized to isophthaUc acid, which is also converted to esters and eventually used in plasticizers and resins (see Phthalic acids and otherbenzenepolycarboxylic acids). 

The baking process has remained much the same until the present day at a stoichiometric ratio of 1 4, phthalic anhydride or phthalic acid reacts with an ammonia releasing compound. The reaction may also start from other suitable materials, such as phthalic acid derivatives, including phthalic acid esters, phthalic acid diamide, or phthalimide. Appropriate ammonia releasing agents include urea and its derivatives, such as biuret, guanidine, and dicyanodiamide. The fact that a certain amount of urea decomposes to form side products makes it necessary to use excess urea. Approximately 0.2 to 0.5, preferably 0.25 equivalents of copper salt should be added for each mole of phthalic anhydride. 0.1 to 0.4 moles of molybdenum salt per mole of phthalic anhydride is sufficient. The reaction temperature is between 200 and 300°C. 

Chemical/Physical. An aqueous solution containing chlorine dioxide in the dark for 3.5 d oxidized naphthalene to chloronaphthalene, 1,4-dichloronaphthalene, and methyl esters of phthalic acid (Taymaz et ah, 1979). In the presence of bromide ions and a chlorinating agent (sodium hypochlorite), major products identified at various reaction times and pHs include 1-bromonaphthalene, dibromonaphthalene, and 2-bromo-l,4-naphthoquinone. Minor products identified include chloronaphthalene, dibromonaphthalene, bromochloronaphthalene, bromo-naphthol, dibromonaphthol, 2-bromonaphthoquinone, dichloronaphthalene, and chlorodibromo-naphthalene (Lin et ah, 1984). 

A racemic alcohol may be converted into a racemic acid by reaction with one molar equivalent of phthalic anhydride the product is a half ester of a dicarboxylic acid (see Section 7.9.1). This can now be subjected to the resolution process for acids and, in due course, the alcohols can be regenerated by hydrolysis of the ester. 

Rubbers. Plasticizers have been used in mbber processing and formulations for many years (8), although phthalic and adipic esters have found litde use since cheaper alternatives, eg, heavy petroleum oils, coal tars, and other predominantly hydrocarbon products, are available for many types of mbber. Esters, eg, DOA, DOP, and DOS, can be used with latex mbber to produce large reductions in T. It has been noted (9) that the more polar elastomers such as nitrile mbber and chloroprene are insufficiently compatible with hydrocarbons and require a more specialized type of plasticizer, eg, a phthalate or adipate ester. Approximately 50% of nitrile mbber used in Western Europe is plasticized at 10—15 phr (a total of 5000—6000 t/yr), and 25% of chloroprene at ca 10 phr (ca 2000 t/yr) is plasticized. Usage in other elastomers is very low although may increase due to toxicological concerns over polynuclear aromatic compounds (9). 

Both anhydrides are prepared in this manner on a large scale for use in the production of ester polymers (Section 29-5A). Phthalic anhydride also is prepared by the oxidation of 1,2-dimethylbenzene ... 

It is important to use rather pure acid esters for the resolution step. The hydrogen phthalates are usually solids that may be crystallized from petroleum ether, benzene, or acetic acid. Phthalic acid is the usual major impurity and may interfere with the crystallization of the ester. If it does, or if the ester is liquid, it is convenient to extract the crude product with chloroform or benzene, in which phthalic acid is nearly insoluble. Distillation of the solvent from the dried extract usually leaves the ester pure enough to crystallize or to use directly. 

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