Benzoic acid cobalt catalysts

It was first described in 1608 when it was sublimed out of gum benzoin. It also occurs in many other natural resins. Benzoic acid is manufactured by the air oxidation of toluene in the liquid phase at 150°C and 4-6 atm. in the presence of a cobalt catalyst by the partial decarboxylation of phthalic anhydride in either the liquid or vapour phase in the presence of water by the hydrolysis of benzotrichloride (from the chlorination of toluene) in the presence of zinc chloride at 100°C. 

The three chemical reactions in the toluene—benzoic acid process are oxidation of toluene to form benzoic acid, oxidation of benzoic acid to form phenyl benzoate, and hydrolysis of phenyl benzoate to form phenol. A typical process consists of two continuous steps (13,14). In the first step, the oxidation of toluene to benzoic acid is achieved with air and cobalt salt catalyst at a temperature between 121 and 177°C. The reactor is operated at 206 kPa gauge (2.1 kg/cm g uge) and the catalyst concentration is between 0.1 and 0.3%. The reactor effluent is distilled and the purified benzoic acid is collected. The overall yield of this process is beheved to be about 68 mol % of toluene. 

Benzoic Acid. Ben2oic acid is manufactured from toluene by oxidation in the liquid phase using air and a cobalt catalyst. Typical conditions are 308—790 kPa (30—100 psi) and 130—160°C. The cmde product is purified by distillation, crystallization, or both. Yields are generally >90 mol%, and product purity is generally >99%. Kalama Chemical Company, the largest producer, converts about half of its production to phenol, but most producers consider the most economic process for phenol to be peroxidation of cumene. Other uses of benzoic acid are for the manufacture of benzoyl chloride, of plasticizers such as butyl benzoate, and of sodium benzoate for use in preservatives. In Italy, Snia Viscosa uses benzoic acid as raw material for the production of caprolactam, and subsequendy nylon-6, by the sequence shown below. 

Acetic acid (qv) can be produced synthetically (methanol carbonylation, acetaldehyde oxidation, butane/naphtha oxidation) or from natural sources (5). Oxygen is added to propylene to make acrolein, which is further oxidized to acryHc acid (see Acrylic acid and derivatives). An alternative method adds carbon monoxide and/or water to acetylene (6). Benzoic acid (qv) is made by oxidizing toluene in the presence of a cobalt catalyst (7). 

Physical and Chemical Properties. The (F)- and (Z)-isomers of cinnamaldehyde are both known. (F)-Cinnamaldehyde [14371-10-9] is generally produced commercially and its properties are given in Table 2. Cinnamaldehyde undergoes reactions that are typical of an a,P-unsaturated aromatic aldehyde. Slow oxidation to cinnamic acid is observed upon exposure to air. This process can be accelerated in the presence of transition-metal catalysts such as cobalt acetate (28). Under more vigorous conditions with either nitric or chromic acid, cleavage at the double bond occurs to afford benzoic acid. Epoxidation of cinnamaldehyde via a conjugate addition mechanism is observed upon treatment with a salt of /-butyl hydroperoxide (29). 

Oxidation catalysts are either metals that chemisorb oxygen readily, such as platinum or silver, or transition metal oxides that are able to give and take oxygen by reason of their having several possible oxidation states. Ethylene oxide is formed with silver, ammonia is oxidized with platinum, and silver or copper in the form of metal screens catalyze the oxidation of methanol to formaldehyde. Cobalt catalysis is used in the following oxidations butane to acetic acid and to butyl-hydroperoxide, cyclohexane to cyclohexylperoxide, acetaldehyde to acetic acid and toluene to benzoic acid. PdCh-CuCb is used for many liquid-phase oxidations and V9O5 combinations for many vapor-phase oxidations. 

Another catalytic system which has been successfully applied to the autoxidation of substituted toluenes involves the combination of Co/Br" with a quaternary ammonium salt as a phase transfer catalyst (ref. 20). For example, cobalt(II) chloride in combination with certain tetraalkylammonium bromides or tetraalkylphosphonium bromides afforded benzoic acid in 92 % yield from toluene at 135-160 °C and 15 bar (Fig. 19). It should be noted that this system does not require the use of acetic acid as solvent. The function of the phase transfer catalyst is presumably to solubilize the cobalt in the ArCH3 solvent via the formation of Q + [CoBr]. ... 

Other routes. Alternate process technologies for making phenol avoid the cumene route. A few plants have used toluene as a feed, oxidizing it over a cobalt catalyst to give benzoic acid. That is followed by a reduction (removal of oxygen atom) to give phenol and carbon dioxide. 

In the United States, benzoic acid is produced commercially by the liquid-phase oxidation of toluene [7,8]. A variety of cobalt catalysts (in the concentration range of 30-1000 ppm) are used for this purpose. 

Benzoic Acid. The industrial-scale oxidation of toluene to benzoic acid is carried out with cobalt catalysts.973,978,982 983 The process, a free-radical autoxidation, is significantly promoted by bromide ions.984 Under these conditions bromine atoms rather than alkylperoxy radicals serve as a regenerable source of chain-initiating free radicals. Substantial rate increase can be achieved by the addition of manga-nese(II) ions.984... 

Liquid-phase oxidation of toluene to benzoic acid (Dow process,980,985,986 Mid-Century process987) may be carried out in acetic acid or without solvent. Cobalt(II) naphthenate or cobalt(II) 2-ethylhexanoate promoted by bromine is used as the catalyst at 140-190°C, at about 8-10 atm pressure. The highly exothermic oxidation is... 

The basic process usually consists of a large reaction vessel in which air is bubbled through pressurized hot liquid toluene containing a soluble cobalt catalyst as well as the reaction products, a system to recover hydrocarbons from the reactor vent gases, and a purification system for the benzoic acid product. 

Catalysts other than the above cobalt salts have been considered. Several patents suggest that cobalt bromide gives improved yields and faster reaction rates (12—16). The bromide salts are, however, very corrosive and require that expensive materials of construction, such as Hastalloy C or titanium, be used in the reaction system. Only one facility, located in the UK, is believed to utilize cobalt bromide catalyst in the production of benzoic acid. 

Benzoic Acid. Benzoic acid is manufactured from toluene by oxidation in the liquid phase using air and a cobalt catalyst. Typical conditions are 308-790 kPa (30-100 psi) and 130-160 C. The crude product is purified... 

Benzoic acid is an important chemical intermediate which can also be used as a phenol precursor by decarbonylation in the presence of copper catalysts (Lummus process). It is produced industrially by oxidation of toluene by air in the presence of cobalt catalysts (Dow and Amoco processes equation 240). The reaction can be carried out without solvent, or in an acetic acid solvent. The oxidation of toluene without solvent uses a cobalt octoate catalyst and operates at higher temperature (180-200 CC). Yields of benzoic acid are about 80% for ca. 50% toluene conversion.361 In an acetic acid solution and in the presence of cobalt acetate, the reaction occurs at lower temperature conditions (110-120 °C) and gives higher yields in benzoic acid (90%).83,84... 

Benzoic acid is synthesized by liquid-phase toluene oxidation over a cobalt naphthenate catalyst with air as the oxidizing agent. An older process involving halogenation of toluene to benzotrichloride and its decomposition into benzoic acid is still used available. 

In this process, cumene is oxidized to cumene hydroperoxide by air at about 100°C in an alkaline environment. The oxidation products are separated, and the bottoms are mixed with a small amount of acetone and sulfuric acid and held at 70-80°C while the hydroperoxide splits into phenol and acetone. Total domestic phenol capacity with this process is about 4.8 billion lb/year. In the much smaller-volume benzoic acid process, toluene is air-oxidized to benzoic acid with a cobalt catalyst. The benzoic acid then is converted to phenol by an oxidative decarboxylation reaction with air at about 240°C. 

Benzoic Acid. Benzoic acid can be produced by the LPO of toluene using a catalyst such as cobalt or manganese. Domestic production of benzoic acid was about 130 million lb in 2000. Of this amount, about one half went to make phenol or phenolic derivatives. Other uses are in the synthesis of caprolactam and terephthalic acid, and as food additive, and as a plasticizer and resin intermediate. 

Benzoic acid is prepared industrially by the oxidation of toluene using air at 170 °C over a catalyst of cobalt and manganese acetate. An alternative route involves the hydrolysis of (trichloromethyl)benzene using aqueous calcium hydroxide in the presence of iron powder as catalyst PhCCl3 is prepared by chlorination of toluene in the presence of light. 

Industrially performed catalytic oxidation reactions often suffer from drawbacks such as poor conversion and selectivity due to overoxidation, corrosive reaction media, lack of solvent and catalyst recycling, and negative environmental impact due to evaporation of the solvents. In order to provide a methodology that addresses these problems, ionic liquids have been investigated as reaction media. For example, the aerobic oxidation of benzyl alcohol and alkylbenzene to benzaldehyde and benzoic acids was performed in l-butyl-2,3-dimethylimidazolium tetrafluoroborate ([C4dmim][BF ]) using palladium and cobalt complexes respectively [34, 35]. 

Jacobsen and co-workers have used similar catalysts in the enantioselective opening of epoxide rings. Stereospecific hydrolysis with a cobalt acetate chelate can be used to resolve racemic epoxides.97 Propylene oxide was opened with trimethylsilylazide in the presence of a 7 7 chromium azide chelate catalyst to produce (5)-l-azido-2-trimethyl-siloxypropane in quantitative yield with 97% ee.98 Cyclohexene oxide was opened with benzoic acid in the presence of 1 mol% cobalt chelate catalyst to give the hydroxyben-zoate in 98% yield with 77% ee.99... 

Benzylic oxidation of aromatic side-chains is also a well established technology in the bulk chemicals arena, e. g. toluene to benzoic acid and p-xylene to ter-ephthalic acid [1,2]. These processes involve homogeneous catalysis by, e. g., cobalt compounds, however, and also fall outside the scope of this book. Ammoxi-dation of methyl-substituted aromatic and heteroaromatic compounds is performed over heterogeneous catalysts in the gas phase but this reaction is treated elsewhere (Section 9.5). Transition metal-substituted molecular sieves have been widely studied as heterogeneous catalysts for oxidation of aromatic side-chains in the liquid phase, but there are serious doubts about their heterogeneity [5,6]. Here again, a cursory examination of the literature reveals that supported palladium seems to be the only heterogeneous catalyst with synthetic utility [4]. 

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