Catalysts in acetic acid

Cyclopropane rings are opened hydrogenolytically, e.g., over platinum on platinum dioxide (Adam s catalyst) in acetic acid at 2 - 4 bars hydrogen pressure. The bond, which is best accessible to the catalyst and most activated by conjugated substituents, is cleaved selectively (W.J. Irwin, 1968 R.L. Augustine, 1976). Synthetically this reaction is useful as a means to hydromethylate C—C double bonds via carbenoid addition (see p. 74f. Z. Majerski, 1968 C.W. Woodworth, 1968). 

A one-step LPO of cyclohexane directly to adipic acid (qv) has received a lot of attention (233—238) but has not been implemented on a large scale. The various versions of this process use a high concentration cobalt catalyst in acetic acid solvent and a promoter (acetaldehyde, methyl ethyl ketone, water). 

Of the three benzenetricarboxyhc acids, only trimellitic acid as the anhydride is commercially produced in large volume, by Hquid-phase air oxidation of either pseudocumene or dimethyl benzaldehyde. The pseudocumene oxidation is another variant of the cobalt—manganese—bromine catalyst in acetic acid solvent as described in the terephthaUc acid section. The acid is available as a laboratory chemical (99). The lUPAC name of trimellitic anhydride is 5-isobenzofurancarboxyhc acid (l,3-dihydro-l,3-dioxo). 

The above generalities apply particularly to palladium. Hydrogenation over platinum or rhodium are far less sensitive to the influence of steric crowding. Reduction of 1-t-butylnaphthalene over platinum, rhodium, and palladium resulted in values of /ci//c2 of 0.42, 0.71, and 0.024, respectively. Also, unlike mononuclear aromatics, palladium reduces substituted naphthalenes at substantially higher rates than does either platinum or rhodium. For example, the rate constants, k x 10 in mol sec" g catalyst", in acetic acid at 50 C and 1 atm, were (for 1,8-diisopropylnaphthalene) Pd (142), Pt(l8.4), and Rh(7.1)(25). 

In the late 1950 s two groups - one at ICI (ref. 1) and the other at the Mid-Century Corporation (ref. 2) - independently discovered that p-xylene is oxidized to terephthalic acid in almost quantitative yield when soluble bromides are used together with cobalt and manganese catalysts in acetic acid solvent at temperatures > 130 °C (ref. 3). This discovery formed the basis for what became known as the Mid-Century process and later, when the Mid-Century Corporation was acquired by Amoco, as the Amoco MC process for the commercial production of terephthalic acid. A large part of the ca. 6 million tons of the latter that are manufactured annually, on a worldwide basis, are produced via this method. This makes it the most important catalytic oxidation process (ref. 4). 

For example, oxidation of substituted toluenes with H2O2 in the presence of a Co /Br catalyst in acetic acid (ref. 25) resulted in the formation of substantial amounts of the corresponding aldehyde (Fig. 22). 

Interestingly, Tanaka (ref. 27) has reported the cooxidation of cyclohexane with acetaldehyde in the presence of a Co(OAc)2 catalyst in acetic acid at 90 °C (3). Adipic acid was obtained in 73% selectivity at 88% cyclohexane conversion. 

Rhodium(I) complexes have also been shown to promote metallo-ene type reactions efficiently (Scheme 7.14) [26]. Typically, the reaction of 2,7-octadienyl-l-carbonate 27 is carried out using the RhH(PPh3)4-tris(2,4,6-trimethoxyphenyl)phosphine system as the catalyst in acetic acid at 80 °C for 1-1.5 h, to give the corresponding l-exo-methylene-2-ethenylcyclopentane 28 in high yield. 

Nitraramine and A-hydroxynitraramine were isolated from Nitraria schoberi (194,195). There are active hydrogen absorption bands in the IR spectrum of nitraramine at 3280 and 3530 cm- and a low intensity band at 1660 cm" (double bond). Acetylation of nitraramine (171) gave A-acetyl and A,0-diacetyl derivatives. Hydrogenation over Adams catalyst in acetic acid gave di-hydronitraramine (172) and dihydrodesoxynitraramine (173) (Scheme 30). The presence of peaks typical for quinolizidine alkaloids in the mass spectra of 171-... 

For both reactions a RhCl3/CH3l/TPO catalyst in acetic acid as reaction solvent affords propionic acid in more than 80 % yield according to the respective stoichiometries of Equations 12 and 13. Although acetic acid is present in excess in the reaction medium, it does not participate in the homologation as reactant. Only traces of propionic acid are produced in the absence of methyl acetate, ethyli-dene diacetate or acetic anhydride under our reaction conditions. Homologation of carboxylic acids has been reported by Knifton (10) to require more severe reaction conditions (220 °C, > 100 bar). 

Hydrogenation of dibenzofuran over a platinum catalyst in acetic acid at 50°C and moderate pressure affords perhydrodibenzofuran. At higher temperatures and pressures with platinum or palladium catalysts the product is 2-biphenylol. When dibenzofuran is hydrogenated in ethanol over Raney nickel at 190°C and 200 atm for 23 h, the products isolated were perhydrodibenzofuran (36%), trans-2-cyclohexylcyclohexanol (27%), cis-2-cyclohexylcyclohexanol (20%), and dicyclohexyl (3%). When the hydrogenation, under these conditions, was terminated after the absorption of only 3 mol equiv of hydrogen, the only product detected was perhydrodibenzo-furan. ° Hydrogenation of dibenzofuran over a sodium-rubidium catalyst,... 

Peracetic acid decomposition kinetics in the presence of cobalt or copper acetates were studied in the same apparatus used for the manganese-catalyzed reaction. However, in these studies it was used as a batch reaction system. The reactor was charged with peracetic acid (ca. 0.5M in acetic acid) and allowed to reach the desired temperature. At this time the catalyst (in acetic acid) was added. Samples were withdrawn and quenched with potassium iodide at measured time intervals. 

Catalytic reduction of 3-methyl-l//-pyrimido [l,2-a]quinoline-l-one (88) over 10% Pd/C catalyst in acetic acid at 50°C atmospheric pressure gave... 

Catalytic hydrogenation of 2-benzyl-4-phenyl-l-oxo-l//-pyrimido[l,2-a]-quinolin-4-ium-3-olate over 5% Pd/C catalyst in acetic acid under 3.5 atm hydrogen at 50°C yielded a 5,6-dihydro derivative (83M227). 

An important advance was made when it was observed that photolysis of the (3-enamido ketone 165, which was readily available from the indoline 163 by Birch reduction followed by N-aryloylation, delivered the lactam 168 as the only photoproduct (Scheme 17) (125). Reduction of 168 with LiAlH4 gave ( )-a-anhydrodihydrocaranine (143), which was then converted to ( )--y-lycorane (93) on hydrogenation over Adams catalyst in acetic acid. In a similar fashion, irradiation of the bromo or iodo enaminones 166 (Z = Br, I), which were obtained by alkylation of the intermediate imino ether formed on Birch reduction of 163, afforded a mixture (approximately 3 2) of the lactam 168 together with the photoreduction product 167 (126). 

Debenzylation with hydrogen in the presence of Pd/C as a catalyst in acetic acid or alcohol/water produces N-hydroxycarbonylmethyl-aminomethyl)alkyl- and -arylphosphinic acids (3)... 

Thoms and Schnupp741 reduced pyrazole itself to pyrazoline, with a palladium catalyst in acetic acid at 20° but this is the only reported catalytic reduction of a pyrazole ring unsubstituted on nitrogen. Under these conditions V-phenyl pyrazoles are converted to V-phenyl-pyrazolines and then at 80° to N-phenylpyrazolidines.741... 

Partenheimer W. The aerobic oxidative cleavage of lignin to produce hydroxyaromatic benzaldehydes and carboxylic acids via metal/bromide catalysts in acetic acid/water mixtures. Adv Synth Catal. 2009 351 456-66. 

Teuber and Schmitt hydrogenated 5-methoxyindole over ruthenium dioxide in 90% ethanol at elevated temperature and pressure and obtained the corresponding octahy-droindole in a 79% yield (eq. 12.9).11 The hydrogenation was difficult to complete with platinum or rhodium-platinum as catalyst in acetic acid. 

Silberman hydrogenated a number of 2,3-dihydro-4//-pyrans substituted in the 2 and 5 positions.220 With Raney Ni, the hydrogenation conditions varied widely, ranging from ready reactions at room temperature to slow hydrogenations at elevated temperatures and pressures. Hydrogenation of 2,5-diethoxycarbonyl-2,3-dihydro-4//-pyran over Raney Ni in ethanol required the conditions of 150°C and 30 MPa H2. Over rhodium or palladium catalysts in acetic acid, hydrogenation could be effected with ease at room temperature and atmospheric pressure (eq. 12.114), while hydrogenation was considerably slowed in an ethanol solution. 

Thiophene 1,1-dioxide with a shielded sulfur atom was hydrogenated without difficulty to the tetrahydro derivative, sulfolane, over palladium catalyst in acetic acid at room temperature and atmospheric hydrogen pressure (eq. 12.121).249... 

Pyrroles may be hydrogenated over a platinum catalyst in acetic acid at 4 atm. and 70° or over a nickel catalyst without solvent at 110 atm. and 180°. N-Substituted pyrroles are more reactive. " " Partial and complete hydrogenation of phenylpyrtoles, phenylindoles, carbazoles, and acridines may be accomplished with either a copper chromite or Raney nickel catalyst. "... 

Catalytic hydrogenation of 2-chloro-3-methylquinoxaline using 5% palladium(II) chloride-charcoal catalyst in acetic acid at 60 °C and 2 atmospheres gives racemic 2-methyl-l,2,3,4-tetrahydroquinoxaline in 65% yield. ... 

The aromaticity of the imidazole nucleus ensures stability towards reduction, and when benzimidazole (27) is hydrogenated over Adams catalyst in acetic acid the carbocyclic ring is reduced first to give the tetrahydrobenzimidazole (28). However, if the solvent is changed to acetic anhydride, A(-acylation promotes the reduction of the heterocycle and the 1,3-diacetylbenzimidazoline (29) is then formed (Scheme 1). Imidazole (30) under these conditions gives 1,3-diacetylimidazoline (31). Imidazolium salts (32) are easily reduced and treatment with excess sodium borohydride in 95% aqueous ethanol culminates in the formation of 1,2-diamines, (33) or (34). Either N—C bond may cleave, although if the substituent R is benzyl the major products are benzylamines (33 R = Bn). ... 

The use of platinum catalysts in acetic acid is not recommended for the removal of halogens from heterocycles as ring hydrogenation also occurs under these conditions. 

Table 2. Oxidation of cresols with palladium-based catalysts in acetic acid / water media... 

Catalytic hydrogenation of 97 with platinum catalyst in acetic acid produced a mixture of stereoisomers, one of them (100) being identical with a tetrahydro compound prepared from solasodine (101). On the basis of the above-mentioned results the structure of veralozidine should be (25R)-22,26-epiminocholesta-5,22(V)-diene-3j8,16j8-diol (97). 

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