Chlorobenzene, decomposition

The most widely used process for the production of phenol is the cumene process developed and Hcensed in the United States by AHiedSignal (formerly AHied Chemical Corp.). Benzene is alkylated with propylene to produce cumene (isopropylbenzene), which is oxidized by air over a catalyst to produce cumene hydroperoxide (CHP). With acid catalysis, CHP undergoes controUed decomposition to produce phenol and acetone a-methylstyrene and acetophenone are the by-products (12) (see Cumene Phenol). Other commercial processes for making phenol include the Raschig process, using chlorobenzene as the starting material, and the toluene process, via a benzoic acid intermediate. In the United States, 35-40% of the phenol produced is used for phenoHc resins. 

When potassium fluoride is combined with a variety of quaternary ammonium salts its reaction rate is accelerated and the overall yields of a vanety of halogen displacements are improved [57, p 112ff. Variables like catalyst type and moisture content of the alkali metal fluoride need to be optimized. In addition, the maximum yield is a function of two parallel reactions direct fluorination and catalyst decomposition due to its low thermal stability in the presence of fluoride ion [5,8, 59, 60] One example is trimethylsilyl fluoride, which can be prepared from the chloride by using either 18-crown-6 (Procedure 3, p 192) or Aliquot 336 in wet chlorobenzene, as illustrated in equation 35 [61],... 

Trichloro- and dichloromethane, ether, dioxane, benzene, toluene, chlorobenzene, acetonitrile, or even pyridine itself has been employed to carry out the one-pot syntheses. Tliese solvents allow straightforward preparation of the salts. The temperature range between 0° and 20°C is usually employed and the salts formed are sufficiently soluble. In the case of slow reactions, selection of a solvent with a higher boiling point is prohtable since thermal instability of the A -(l-haloalkyl)heteroarylium halides has not been reported. Addition of water or an aqueous solution of sodium acetate does not cause a rapid decomposition of the salts so that this constitutes a useful step in the optimization of some procedures. 

Meso- and (+ )-azobis[6-(6-cyanododecanoic acid)] were synthesized by Porter et al. (1983) as an amphipathic free radical initiator that could deliver the radical center to a bilayer structure controllably for the study of free radical processes in membranes. The decomposition pathways of the diazenes are illustrated in Fig. 36. When the initiator was decomposed in a DPPC multilamellar vesicle matrix, the diazenes showed stereo-retention yielding unprecedented diastereomeric excesses, as high as 70%, in the recombination of the radicals to form meso- and (+ )-succinodinitriles (Brittain et al., 1984). When the methyl esters of the diazene surfactants were decomposed in a chlorobenzene solution, poor diastereoselectivity was observed, diastereomeric excesses of 2.6% and 7.4% for meso- and ( )-isomers respectively, which is typical of free radical processes in isotropic media (Greene et al, 1970). 

In the case of cobalt ions, the inverse reaction of Co111 reduction with hydroperoxide occurs also rather rapidly (see Table 10.3). The efficiency of redox catalysis is especially pronounced if we compare the rates of thermal homolysis of hydroperoxide with the rates of its decomposition in the presence of ions, for example, cobalt decomposes 1,1-dimethylethyl hydroperoxide in a chlorobenzene solution with the rate constant kd = 3.6 x 1012exp(—138.0/ RT) = 9.0 x 10—13 s—1 (293 K). The catalytic decay of hydroperoxide with the concentration [Co2+] = 10 4M occurs with the effective rate constant Vff=VA[Co2+] = 2.2 x 10 6 s— thus, the specific decomposition rates differ by six orders of magnitude, and this difference can be increased by increasing the catalyst concentration. The kinetic difference between the homolysis of the O—O bond and redox decomposition of ROOH is reasoned by the... 

Rate Constants of Bimolecular Catalytic Decomposition of Hydroperoxides Under Action of Products of Oxidation of S-Containing Compounds in Chlorobenzene (Experimental Data)... 

Crude sulfur vesicants are relatively stable and stability increases with purity Distilled materials show very little decomposition on storage. Solvents such as carbon tetrachloride and chlorobenzene have been added to enhance stability of crude material. Agents can be stored in glass or steel containers, although pressure may develop in steel containers. Sulfur vesicants rapidly corrode brass and cast iron, and permeate into ordinary rubber. 

Increase in electron availability (as measured by the ionisation potential) within the target olefin does indeed increase the rate of addition. Electron withdrawing groups (m-CN, m-Cl) in the nitrobenzene moiety stabilized the adducts, whereas an increased rate of decomposition was observed with adducts from p-chlorobenzene and m- or p-nitrotoluene... 

A versatile new and general method was developed for the synthesis of six-membered 1,3-heterocycles. In comparison with the general reaction conditions of retrodiene reactions, a very mild retro Diels-Alder (RDA) decomposition was found to occur when the norbornene-d/eAro- or -diendo-fused dihydrooxazinone 474 was heated at melting temperature or refluxed in different solvents (e.g., chlorobenzene). Cyclopentadiene splitt off and the 2-aryl-6//-l,3-oxazin-6-ones 475, earlier unknown representatives of the simple 1,3-oxazines, were obtained (84S345, 84T2385). 

While some phenol is produced by the nucleophilic substitution of chlorine in chlorobenzene by the hydroxyl group (structure 17.17), most is produced by the acidic decomposition of cumene hydroperoxide (structure 17.18) that also gives acetone along with the phenol. Some of the new processes for synthesizing phenol are the dehydrogenation of cyclohexanol, the decarboxylation of benzoic acid, and the hydrogen peroxide hydroxylation of benzene. 

Alkyl-5-picrylimino-l,2,3,4-thiatriazolines are exceptionally thermostable. The 4-benzyl and 4-isopropyl derivative did not thermolyze at 90 °C in chlorobenzene or toluene decomposition started only after prolonged heating at 105 °C and was complete after 3-5 days. The resulting mixtures showed no IR spectroscopic evidence of carbodiimide formation <90JHC1059>. 

Charge-separated two-bond rupture has been observed during thermal decomposition of ferf-butyl phenylperacetates and related reactions ". Homolysis of ferf-butyl phenylper-acetates in chlorobenzene shows better correlation with a+ to give p+ = -1-1.04 at... 

Decomposition of 3,4,5,6-tetrachlorobenzene-2-diazo 1-oxide (68, Scheme 17) in chlorobenzene at 130°C presumably involves the ketocarbene 69 and yields some of the dibenzofuran 72 via the 2 -chloro-2-biphenylol 71 because its isomer (70) is also a product. 

Slight decomposition during the reaction indicated by formation of grey-green precipitates was found difficult to avoid with chlorobenzene and some other arenes. This appears to become progressive and reaction should be stopped and solutions filtered when such precipitation is observed. Solvent dibutyl ether (60 itiL) + tetrahydrofuran (5 mL) most of the product from this reaction crystallized from the solution when cooled in ice. 

Similar decomposition is observed in p-bromoacetophenone, o-bromo-, p-bromo, and p,p -dibromobenzophenone, and p-iodobenzophenone44 but not in the fluoro- and chloro-substituted compounds. This order of reactivity follows the bond dissociation energies for aromatic halides which are about 90 kcal/mole for chlorobenzene, 70 kcal/mole for bromobenzene, and 60 kcal/ mole for iodobenzene. The lowest-lying triplet of p-bromoacetophenone is 71.2 kcal45 while that of the substituted benzophenones is slightly lower since benzophenone itself has a lower triplet energy than acetophenone. p,p Dibromobenzophenone was the least reactive of the compounds that photoeliminated halogen atoms. 

However, bromobenzene and chloroaromatics (chlorobenzene, 1,2-dichlorobenzene, 1,2,4-trichlorobenzene) are inert enough to be used routinely,131 181 222-223 except when the aryl cation generated during dediazoniation is stable enough to arylate the aromatic solvents.137 The advantage of pyrolysis in chlorobenzene over dry decomposition has been illustrated in the synthesis of mono- and difluorobenzo[c]phenanthrenes.230... 

E.R. Ritter, J.W. Bozzelli, and A.M. Dean. Kinetic-Study on Thermal-Decomposition of Chlorobenzene Diluted in H2. J. Phys. Chem., 94 2493-2504,1990. 

Ammonia decomposes on zeolites (9), and the effect of this decomposition on the chlorobenzene reaction may be important. Thus, the activity of CuY zeolite for ammonia decomposition was studied. Helium was used as a carrier gas, 1 ml of ammonia was injected, and the extent of ammonia decomposition was determined as a function of temperature. The decomposition was 2.4% at 350°C, 7.8% at 450° C, and 24% at 550° C. The apparent activation energy of ammonia decomposition was estimated at 13 kcal/mole. The activation energy of ammonia decomposition is close to that of benzene formation from chlorobenzene and ammonia. Thus, benzene formation results from the reaction of chlorobenzene and hydrogen formed by the decomposition of ammonia. 

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