Phthalic anhydride purification

The crude phthalic anhydride is heated and held at 260 C to allow some byproduct reactions to go to completion. Purification is by continuous distillation in two columns. In the first column, maleic anhydride and benzoic and toluic acids are removed overhead. In the second column, pure phthalic anhydride is removed overhead. High boiling residues are removed from the bottom of the second column. 

Phthalic Anhydride Recovery and Purification. The accepted method of recovering phthalic anhydride from vapor-phase oxidation... 

An improved method for the synthesis of 4-hydroxy-1-oxo-l,2-dihydroisoquinoline-3-carboxylic acid derivatives 130 was presented <06S1971>. This improved three-step method efficiently converts phthalic anhydride 131 to the desired dihydroisoquinolines 130 in high yields over three steps with only one purification. 

The phthalic anhydride/urea process may also be employed to convert tetra-chloro phthalic anhydride to green copper hexadecachloro phthalocyanine by condensation. In this case, titanium or zirconium dioxides, particularly in the form of hydrated gels, are used instead of the molybdenum salts which are used in the phthalic anhydride process [23]. There is a certain disadvantage to the fact that the products lack brilliance and require additional purification. 

Anhydrides. The corresponding acids, resulting from hydrolysis, are the most likely impurities. Distillation from phosphorus pentoxide, followed by fractional distillation, is usually satisfactory. With high boiling or solid anhydrides, another method involves refluxing for 0.5-1 hour with acetic anhydride, followed by fractional distillation. Acetic acid distils first, then acetic anhydride and finally the desired anhydride. Where the anhydride is a solid, removal of acetic acid and acetic anhydride at atmospheric pressure is followed by heating under vacuum. The solid anhydride is then either crystallised as for acid chlorides or (in some cases) sublimed in a vacuum. A preliminary purification when large quantities of acid are present in a solid anhydride (such as phthalic anhydride) can sometimes be... 

Phthalic anhydride, 681, 753, 984, 985 purification of, 507 Phthalide, 753, 772 Phthalimide, 753, 754, 771 Phthalimides, N-substituted, 423 Phthalonitrile, 983 Phthalylacetic acid, 995 Physical constants, determination of, 1028-1037... 

Commercial phthalic anhydride, purchased from Wako Pure Chemical Industries, Ltd. (Japan) or from Fluka AG, Buchs (Switzerland), was used without purification. 

Derivation By treating n-butyl alcohol with phthalic anhydride followed by purification, which results in a product unusually free from odor and color. 

Derivation By reacting phthalic anhydride with ethanol followed by careful purification. 

Purification. R. Breslow and J. Posner [Org. Syn., 47,62 (1967)] recommend that commercial triethylamine be purified to remove primary and secondary amines and water either by distillation from acetic anhydride and then from barium oxide or by reaction with phenyl isocyanate. F. F. Rogers, Jr., R. J. Albers, and D. F. DeTar (procedure submitted to Org. Syn.) recommend refluxing with phthalic anhydride followed by distillation. 

The heat of reaction.is removed by water circulation in tubes placed in the catalytic bed, with the production of 4ngb pressure steam. Solid partides entrained by the gas stream leaving the reactor are retained on a series of ceramic fibers and returned to the reaction medium. The phthalic anhydride formed is condensed m the liquid and solid state. It is then sent to the purification section, where it is subjected to heat treatment interned to decompose the nonvolatile impurities liable to dye the final product, and then to vacuum distillation. The phthalic anhydride yields are not as high as those of fixed bed processes, especially those starting with o-xylene. 

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