Synthesis of phthalic anhydride

Preparation of phthalic anhydride

Preparation of phthalic anhydride

Preparation of phthalic anhydride

The catalytic oxidation of naphthalene can easily be carried out in the laboratory. It is of great importance that the correct temperature be maintained and that a suitable catalyst be used. Special attention must be given to the apparatus if the preparation in the laboratory is to succeed. Furthermore, it is highly desirable to use a Cottrel precipitator to collect the reaction product completely. This apparatus will collect even the fine particles, which otherwise would be lost.

Preparation of the Catalyst
Pumice is broken up into pieces about 3 mm. in size and screened, using a sieve that retains the 3-mm. pieces. The more uniform the pieces are, the better. This pumice is placed in a hot solution of ammonium vanadate which is as concentrated as possible. When the pumice is thoroughly impregnated, it is removed from the solution and dried in a porcelain dish on a water bath. About 3 grams of vanadium are taken up by 200 grams of pumice. The dried mass is now heated to 400°C. until the grains have a reddish brown color. It is important that the catalyst is not heated above the temperature at which it is to be used later, a precaution to be observed in many catalytic reactions.

Performing the Reaction. Apparatus

A glass apparatus for the preparation of phthalic anhydride

Apparatus for preparation of phthalic anhydride by catalytic oxidation: A, air inlet tube; B, melted naphthalene; C, graphite bath; D, electrical heating element; E, ground; F, spark induction coil; G, glass wool; H, catalyst; J, bulb receiver; K, aluminum foil, grounded; L, gas exit tube; M, thermocouple; N, rigid wire; Th, thermometer. One side of the spark induction coil is connected to N, the other is grounded.


Naphthalene is placed in flask B, which is heated to 110°C., and a stream of moist air is passed through the gas introduction tube (A). The presence of water vapor is important for the oxidation. The necessary air is most simply supplied by a water pump and the quantity of air passed through the apparatus is measured with regular laboratory equipment. The air stream should be regulated so that 200 liters of air and 5 grams of naphthalene are passed through the apparatus in 1 hour. It is important that the ratio of air to naphthalene be controlled so that an explosive mixture is not formed. The mixed gases (air and naphthalene vapor) are passed into the catalyst tube, which should be of about 5-cm. internal diameter and should contain a charge of catalyst about 10 cm. in length. The pumice particles are held in place by glass wool. Heating of the catalyst is done electrically as is the usual practice in technical laboratories. The gases coming from the catalyst are passed first into a round receiver (J), and then go to the precipitator. The latter consists of a glass tube of about 8-cm. internal diameter, the inside wall of which is lined with a smooth aluminum foil which can be removed easily and which is well grounded through a metal wire to a water pipe. A wire or silvered glass rod projects into the tube, and to this a potential of 10,000 volts is applied. This potential, which can be alternating for the present purpose, is generated in the usual manner, most simply by an induction coil or a transformer with interrupter. It is important that the air spark length of the induction coil be at least 25 mm. The internal width of the tube carrying the precipitator must therefore be sufficiently great so that sparks do not jump from the wire to the metal foil. Such sparking may cause explosions which, although not involving danger, may easily burn part of the reaction product. When the apparatus, to which careful attention must be given, is assembled correctly, the oxidation can be started. The catalyst tube is heated to 450°C. (thermocouple), and the stream of mixed air and naphthalene vapor is started. The oxidation takes place as the vapors pass through the catalyst. Part of the phthalic anhydride collects in the bulb receiver, but most of it is collected in the Cottrel precipitator where it frequently forms beautiful needles, up to 5 cm. in length, in a small space at the extreme first part of the precipitator. The operation can be continued as long as desired, since the catalyst retains its activity for weeks provided that pure naphthalene is used. The yield of phthalic anhydride is about 90 to 95 % of the theoretical amount, the product being chemically pure if the oxidation temperature is maintained at the correct point and the throughput is not too high. If too much naphthalene is put through per unit of time, the product becomes yellowish due to admixed 1,4-naphthoquinone. The product is removed from time to time by drawing out the aluminum foil. 20 grams of pure phthalic anhydride can easily be prepared in 5 hours in the laboratory.

The fundamental processes of dye chemistry, by H. E. Fierz-David, 171-173, 1949





InChI Key


Canonical SMILES


MeSH Synonyms

1,2-benzenedicarboxylic anhydride, 1,3-isobenzofurandione, phthalic acid anhydride, phthalic anhydride, phthalic anhydride, 14C-labeled cpd

Depositor-Supplied Synonyms

PHTHALIC ANHYDRIDE, Isobenzofuran-1,3-dione, 1,3-Isobenzofurandione, 85-44-9, Phthalic acid anhydride, 1,3-Dioxophthalan, 1,3-Phthalandione, 2-Benzofuran-1,3-dione, Phthalsaeureanhydrid, Phthalandione, o-Phthalic acid anhydride, Retarder esen, Retarder AK, Retarder PD, Vulkalent B/C, ESEN, Anidride ftalica, Ftaalzuuranhydride, Ftalowy bezwodnik, Anhydride phtalique, 1,2-Benzenedicarboxylic acid anhydride, 1,2-Benzenedicarboxylic anhydride, Ftalanhydrid, phtalic anhydride, Vulkalent B, NCI-C03601, Wiltrol P, RCRA waste number U190, TGL 6525, Ftalanhydrid [Czech], CHEBI:36605, Anhydrid kyseliny ftalove, NSC 10431, Ftaalzuuranhydride [Dutch], RCRA waste no. U190, UNII-UVL263I5BJ, Anidride ftalica [Italian], Ftalowy bezwodnik [Polish], Phthalic anhydride (molten), Anhydride phtalique [French], ortho-phthalic acid anhydride, Isobenzofuran, 1,3-dihydro-1,3-dioxo-, Phthalsaeureanhydrid [German], CCRIS 519, 1,3-Isobenzofurandione,oxidized, HSDB 4012, Anhydrid kyseliny ftalove [Czech], LGRFSURHDFAFJT-UHFFFAOYSA-N, EINECS 201-607-5, UN2214, 1,3-dihydro-2-benzofuran-1,3-dione, AI3-04869, PHTHALIC-D4 ANHYDRIDE, 39363-63-8, 68411-80-3, Phthalanhydride, Phthalicanhydride, pthalic anhydride, Retarder PX, Sconoc 7, 1,3 Phthalandione, Araldite HT 901, PubChem17494, Phthal ic acid anhydride, AC1L1NCV, isobenzofurane-1,3-dione, DSSTox_CID_1159, SCHEMBL220, Epitope ID:112744, WLN: T56 BVOVJ, AC1Q6H7L, Phthalic anhydride, oxidized, DSSTox_RID_75982, UVL263I5BJ, DSSTox_GSID_21159, Isobenzo[b]furan-1,3-dione, 2-Benzofuran-1,3-dione #, UN 2214 (Salt/Mix), Phthalic anhydride treated BSA, Phthalic anhydride treated HSA, ACMC-209q60, 125733_ALDRICH, CHEMBL1371297, 80020_FLUKA, CTK3E8282, Ht 901, 1,3-Isobenzofurandione, oxidized, MolPort-000-006-132, Phthalic anhydride treated gelatin, Phthalic anhydride treated casein I, 125733_SIAL, 320064_SIAL, ACT03366, NSC10431, ZINC8100883, EINECS 270-149-6, Phthalic anhydride treated casein II, Tox21_200142, 1,3-dihydro-1,3-dioxoisobenzofuran, 1,3-dihydroisobenzofuran-1,3-dione, ANW-38182, Isobenzofuran,3-dihydro-1,3-dioxo-, MFCD00005918, NSC-10431, SBB040869, AKOS000121309, LS-1848, MCULE-5260748273, NE10417, RP21190, RTR-026706, CAS-85-44-9, NCGC00091060-01, NCGC00091060-02, NCGC00257696-01, AK114446, AN-42311, BP-30002, HE000911, HE264977, HE386497, HE397234, HE397235, K528, SC-46773, AB1002188, KB-254430, ST2413139, FT-0652549, P1614, ST50214459, Phthalic anhydride treated human serum albumin, 7788-EP2269992A1, 7788-EP2272517A1, 7788-EP2277878A1, 7788-EP2295503A1, 7788-EP2301911A1, 7788-EP2302015A1, 7788-EP2305248A1, 7788-EP2308844A2, 7788-EP2308845A2, 7788-EP2308846A2, 7788-EP2308865A1, 7788-EP2309584A1, 7788-EP2311824A1, 7788-EP2314593A1, 7788-EP2316905A1, 7788-EP2316906A2, 7788-EP2371805A1, 7788-EP2371831A1, P60058, Phthalic anhydride treated bovine serum albumin, Phthalic anhydride treated rabbit serum albumin, Phthalic anhydride with >0.05% maleic anhydride, A841333, 3B4-0897, I14-2753, Phthalic anhydride treated-reduced and alkylated BSA, 3B1-007931, 1,3-Isobenzofurandione; Benzene-1,2-dicarboxylic anhydride, Phthalic anhydride treated-reduced and alkylated bovine serum albumin, Rosin, polymer with pentaerythritol, phthalic anhydride and tall oil, InChI=1/C8H4O3/c9-7-5-3-1-2-4-6(5)8(10)11-7/h1-4, Phthalic anhydride with >0.05% maleic anhydride [UN2214] [Corrosive], Phthalic anhydride with >0.05% maleic anhydride [UN2214] [Corrosive]

Removed Synonyms

C8H4O3, CID6811, phthalic anhydride, 14C-labeled cpd, T1243, C043103, Pan,

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