Amines, cracking reactions

Tanabe and Hdlderich (1999) have given an extensive statistical survey of industrial processes using solid acids/bases as catalysts. Over 300 solids and bases have been covered. A variety of reactions like alkylation, isomerization, amination, cracking, and etherification with catalysts like zeolites, oxides, complex oxides, phosphates and ion-exchange resins have been covered. Over 120 industrial processes are referred with 180 different catalysts. 

As has been mentioned previously, one is most likely to find analogies to catalytic reactions on solids with acidic and/or basic sites in noncatalytic homogeneous reactions, and therefore the application of established LFERs is safest in this field. Also the interpretation of slopes is without great difficulty and more fruitful than with other types of catalysts. The structure effects on rate have been measured most frequently on elimination reactions, that is, on dehydration of alcohols, dehydrohalogenation of alkyl halides, deamination of amines, cracking of the C—C bond, etc. Less attention has been paid to substitution, addition, and other reactions. 

Recent reviews (31-34,36,37,51) provide a comprehensive survey of the types of heterogeneous catalytic reactions investigated at supercritical conditions including alkylation, amination, cracking, disproportionation, esterification, Fischer-Tropsch synthesis, hydrogenation, isomerization, and oxidation. Table 2 summarizes reported investigations under these classes of reaction. Some of these examples are described here to show how to systematically exploit supercritical media in heterogeneous catalysis. 

Other components in the feed gas may react with and degrade the amine solution. Many of these latter reactions can be reversed by appHcation of heat, as in a reclaimer. Some reaction products cannot be reclaimed, however. Thus to keep the concentration of these materials at an acceptable level, the solution must be purged and fresh amine added periodically. The principal sources of degradation products are the reactions with carbon dioxide, carbonyl sulfide, and carbon disulfide. In refineries, sour gas streams from vacuum distillation or from fluidized catalytic cracking (FCC) units can contain oxygen or sulfur dioxide which form heat-stable salts with the amine solution (see Fluidization Petroleum). 

Polyisobutylene has the chemical properties of a saturated hydrocarbon. The unsaturated end groups undergo reactions typical of a hindered olefin and are used, particularly in the case of low mol wt materials, as a route to modification eg, the introduction of amine groups to produce dispersants for lubricating oils. The in-chain unsaturation in butyl mbber is attacked by atmospheric ozone, and unless protected can lead to cracking of strained vulcanizates. Oxidative degradation, which leads to chain cleavage, is slow, and the polymers are protected by antioxidants (75). 

Certain internal chemical treatments employed also need strict control to avoid risks of adverse chemical reaction and resultant corrosion. In particular, nitrogen-containing chemicals such as hydrazine and amines require effective monitoring to limit the concentration of ammonia release into steam because the presence of ammonia may, under certain conditions, cause stress corrosion cracking of copper and brasses. 

Thus hydrochloric acid is a derivative of chlorine. About 93% of it is made by various reactions including the cracking of ethylene dichloride and tetrachloroethane, the chlorination of toluene, fluorocarbons, and methane, and the production of linear alkylbenzenes. It is also a by-product of the reaction of phosgene and amines to form isocyanates. 

To 450 cc. of concentrated hydrochloric acid (sp. gr. 1.19) and 500 cc. of water in a 4-I. (i-gal.) earthenware crock equipped with an efficient stirrer is added 143 g. (1 mole) of /3-naphthyla-mine. The suspension of the amine hydrochloride is cooled by the addition of 500 g. of cracked ice. When the temperature reaches 5° solid sodium nitrite (about 69 g.) is added until starch-iodide paper shows an excess. During the diazotization about 600 g. of cracked ice is introduced at such a rate as to keep the temperature at 50. The cold solution of the diazonium salt is filtered to remove a small amount of precipitate and returned to the crock. A solution of 271 g. (1 mole) of mercuric chloride in 300 cc. of concentrated hydrochloric acid is mixed with 300 g. of ice and added slowly to the rapidly stirred solution. A heavy yellow solid separates. Stirring is continued for one-half hour to secure complete reaction. The yellow addition compound of /3-naphthalene diazonium chloride and mercuric chloride is collected on a 20-cm. Buchner funnel, sucked as dry as possible, and then washed with two 400-cc. portions of water and two 150-cc. portions of acetone (Note 1). The... 

Ethylene-Based (C-2> Routes. MMA and MAA can be produced from ethylene as a feedstock via propanol, propionic acid, or melhyl propionate as intermediates. Propanal may be prepared by hydrofonnylalion of ethylene over cobalt or rhodium catalysts. The propanal then reads in the liquid phase with formaldehyde in the presence of a secondary amine and. optionally, a carboxylic acid. The reaction presumably proceeds via a Mannich base intermediate which is cracked to yield methacrolcin. Alternatively, a gas-phase, crossed akin I reaelion with formaldehyde cataly zed by molecular sieves [Pg.988]

Isocyanates may be prepared via a number of routes, including the thermal cracking of urethanes or silylurethanes [107], or the reaction of N-alkylcarbamate esters with boron trichloride [108] or chloroboranes [109] or chorosilanes [110] in the presence of bases (NEt3). To date, however, only amine phosgenation is practiced on a significant industrial scale [10, 106],... 

To a solution of 4.0 g of 1,4-naphthoquinone in 800 mL (31.6 x 10 M) ethanol/triethyl-amine (50 50) in a pyrex tube, 0.8 g of freshly cracked cyclopentadiene (15.1 x 10" M) was added and the reaction mixture was purged with a slow stream of nitrogen for 10 min. Above solution was irradiated at 300 nm in a Rayonet photochemical reactor with constant stirring and cooling at room temperature for 6 h. Progress of the reaction was monitored by TLC and GC, until more than 95% of the dienophile is consumed. After removal of the solvent and triethylamine under reduced pressure, the residue was chromatographed over silica gel (60-120 mesh). Elution with 5% acetone/hexane gave 2.44 g (43%) of 3.3, mp 160 °C. 

In the sequence of reactions shown in Figure 1, the chain scission reactions of the alkoxy radical PO are important in the formation of a crack and thus embrittlement. The reactions in the presence of the nitroxide and hindered phenol stabilizers are modified by competition with the stabilization reactions that lead to either an inert, non-radical alkoxy amine product (R2NOP) or, for a hindered phenol, a stable radical (A-) that cannot initiate further oxidation. 

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