Process for preparing phthalides

Details Process for preparing phthalides Process for preparing phthalides

1999-01-07

2000-02-01

Owens, Amelia

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

549305, 549310, C07D30783

Patent

active

060205016

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

The present invention relates to a process for preparing phthalides by catalytic hydrogenation of phthalic anhydrides with the aid of nickel catalysts doped with metals of subgroup Ib, subgroup VIb and/or subgroup VIIB of the Periodic Table.
DE-C-28 03 319 discloses a process for preparing phthalide by catalytic hydrogenation of phthalic anhydride in the gas phase using copper- and aluminum-containing catalysts. However, this process is prohibitively costly at the product isolation stage, involving as it does multistage condensation and a downstream waste gas scrub. EP-A-542 037 describes a process for preparing phthalides by catalytic hydrogenation of phthalic anhydride over fixed bed catalysts. This process needs large quantities of catatlyst and long hydrogenation times when practiced batchwise and high pressures to achieve complete conversion when practiced continuously.
U.S. Pat. Nos. 4,485,246 and 3,957,825 disclose that it is possible to prepare phthalide from phthalic anhydride by hydrogenation with homogeneous ruthenium catalysts. Catalyst recovery is difficult in these processes.
EP-B-89 417 describes the catalytic hydrogenation of phthalic anhydride to phthalide with the aid of a nickel catalyst immobilized on a support material using methyl benzoate as mandatory solvent. The process has the disadvantage of high catalyst requirements and long reaction times.
It is further known from Houben/Weyl, Methoden der organischen Chemie, 6/2 (1963), 732 to 733, to hydrogenate phthalic anhydride to phthalide with the aid of Raney nickel as catalyst, but a hydrogen pressure of 165 bar and ethanol as solvent affords a phthalide yield of only 73%.
It is an object of the present invention to remedy the aforementioned disadvantages of using existing catalysts in the catalytic hydrogenation of phthalic anhydrides.
We have found that this object is achieved by a novel and improved process for preparing a phthalide of the general formula I ##STR3## where R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each independently of the others hydrogen, C.sub.1 -C.sub.4 -alkyl or C.sub.1 -C.sub.4 -alkoxy, by hydrogenation of a phthalic anhydride of the general formula II ##STR4## where R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each as defined above, with the aid of a hydrogenation catalyst, which comprises performing the hydrogenation with the aid of a nickel catalyst doped with metals of subgroup 1, subgroup 6 and/or subgroup 7 of the Periodic Table.
The process of the invention makes it possible to perform the hydrogenation of phthalic anhydrides to phthalides at low levels of catalyst, with a good space-time yield and in high selectivity. The catalysts to be used according to the invention have distinctly increased activity compared with conventional Raney nickel. This leads to milder reaction conditions or, under the customary reaction conditions for undoped Raney nickel, to faster hydrogenation and hence to higher space-time yields.
Compared with the catalysts to be used in the process described in EP-A-542 037, the catalysts to be used according to the invention likewise have distinctly increased activity. Whereas the known process generally produces only incomplete conversions after 12 hours' hydrogenation and 260 bar pressure using 10% of catalyst, based on the phthalic anhydride used, despite the use of high reaction temperatures of from 150 to 250.degree. C., the process of the invention affords virtually complete conversion under milder reaction conditions and in a shorter time.
The catalytic hydrogenation is generally carried out at temperatures from 50 to 400.degree. C., preferably from 100 to 250.degree. C., especially from 140 to 220.degree. C., and pressures from 1 to 400 bar, preferably from 5 to 300 bar, especially from 5 to 200 bar, particularly advantageously from 30 to 120 bar.
Customary hydrogenation reactors can be used, for example autoclaves or tubular reactors.
The hydrogenation catalysts used for the process of the invention are nickel catalysts doped with metals of subgroup Ib of the Perio

REFERENCES:
patent: 3957825 (1976-05-01), Urry et al.
patent: 3997478 (1976-12-01), Petro
patent: 4485246 (1984-11-01), Lyons
patent: 4528385 (1985-07-01), Fuenten et al.
patent: 5296614 (1994-03-01), Henkelmann et al.
Houben-Weyl, Methoden der organischen Chemie, Jun. 2, 1963, pp. 732-733 (translation).

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