Side reactions alkylation

Alkylator, side reactions in, 23 329 Alkylbenzene(s), 12 162, 163, 169 23 329 from benzene, 3 619t, 620 biodegradation, 3 763t by-products, 23 335 dispersant moieties, 8 706t formylation of, 12 178 oxidation of, 26 894-896 Alkylbenzenesulfonates, rat oral LD50 values, 3 445... 

Fig. 6 Possible alkylation side reactions. (View this art in color at www.dekker.com.)...

In many literature procedures for reductive alkylations (of primary amines), concerns over the bis-alkylation side reaction to give the tertiary amine are evident It is claimed that this type of problem does not affect the procedures described above [30]. For reactions with isocyanates, the best results are obtained with a chlorinated solvent (CH2CI2). Isothiocyanates give optimum yields when heated to reflux in acetonitrile. 

In this reaction, partial racemization of some homochiral amino acids was observed. In addition, the combination of a hindered amino acid and an electronically deactivated aldehyde may lead to low yields. Bis-alkylation side reactions of aliphatic aldehydes may generate 1-10% of tertiary amines. 

Of those in common usage, the 2-chlorotrityl 28 [74] and 4-carboxytrityl 29 [75] linkers give the least stabilized cations and are suitable for immobilization of carboxylic acids. They are ideal for Fmoc/tBu-based SPPS as their use avoids many of the side reactions that occur with standard benzyl-based linkers. Firstly, race-mization does not occur during loading of the resin with the C-terminal residue [79], as is the case with esterification to hydroxy-functionalized resins. Secondly, the bulky trityl cation does not cause alkylation side reactions with nucleophilic amino-acid side-chains. Thirdly, cysteine does not undergo racemization [80, 81]... 

Alkyl and aryl iodides usually react with magnesium more rapidly than the corresponding bromides, and the bromides very much more rapidly than the chlorides. Aryl (as distinct from alkyl) chlorides have usually only a slow reaction with magnesium and are therefore very rarely used. With alkyl and aryl iodides in particular, however, a side reaction often occurs with the formation of a hydrocarbon and magnesium iodide ... 

The percentage of cyclohexylation is given in Fig. 1-20. (411,412). Hydrogen abstraction from the alkyl side-chain produces, in addition, secondary products resulting from the dimerization of thiazolylalkyl radicals or from their reaction with cyclohexyl radicals (Scheme 68) (411). 

The reactivity of alkylthiazoles possessing a functional group linked to the side-chain is discussed here neither in detail nor exhaustively since it is analogous to that of classical aliphatic and aromatic compounds. These reactions are essentially of a synthetic nature. In fact, the cyclization methods discussed in Chapter II lead to thiazoles possessing functional groups on the alkyl chain if the aliphatic compounds to be cyclized, carrying the substituent on what will become the alkyl side chain, are available. If this is not the case, another functional substituent can be introduced on the side-chain by cyclization and can then be converted to the desired substituent by a classical reaction. 

Benzene with no alkyl side chain and no benzyhc hydrogens undergoes a different reaction under these conditions Oxidation of the ring occurs to convert benzene to its epoxide... 

A primary or secondary alkyl side chain on an aromatic ring is converted to a carboxyl group by reaction with a strong oxidizing agent such as potassium permanga nate or chromic acid... 

There are two important side reactions, particularly above 120°C (/) aluminum alkyls decompose to form diaLkylalurninum hydrides and alpha olefins (the diaLkylalurninum hydrides rapidly react with ethylene to regenerate a trialkylalurninum) ... 

Tocotrienols differ from tocopherols by the presence of three isolated double bonds in the branched alkyl side chain. Oxidation of tocopherol leads to ring opening and the formation of tocoquinones that show an intense red color. This species is a significant contributor to color quaUty problems in oils that have been abused. Tocopherols function as natural antioxidants (qv). An important factor in their activity is their slow reaction rate with oxygen relative to combination with other free radicals (11). 

Fig. 7. Reactions of ttiglycetides at the carbonyl ester linkage. R represents the alkyl side chain.

An important side reaction in all free-radical nitrations is reaction 10, in which unstable alkyl nitrites are formed (eq. 10). They decompose to form nitric oxide and alkoxy radicals (eq. 11) which form oxygenated compounds and low molecular weight alkyl radicals which can form low molecular weight nitroparaffins by reactions 7 or 9. The oxygenated hydrocarbons often react further to produce even lighter oxygenated products, carbon oxides, and water. 

Thermal, Thermooxidative, and Photooxidative Degradation. Polymers of a-olefins have at least one tertiary C-H bond in each monomer unit of polymer chains. As a result, these polymers are susceptible to both thermal and thermooxidative degradation. Reactivity in degradation reactions is especially significant in the case of polyolefins with branched alkyl side groups. For example, thermal decomposition of... 

Unsymmetrical dialkyl peroxides are obtained by the reaction of alkyl hydroperoxides with a substrate, ie, R H, from which a hydrogen can be abstracted readily in the presence of certain cobalt, copper, or manganese salts (eq. 30). However, this process is not efficient since two moles of the hydroperoxide are consumed per mole of dialkyl peroxide produced. In addition, side reactions involving free radicals produce undesired by-products (44,66). 

A simplified flow diagram of a modern H2SO4 alkylation unit is shown in Eigure 1. Excess isobutane is suppHed as recycle to the reactor section to suppress polymerization and other undesirable side reactions. The isobutane is suppHed both by fractionation and by the return of flashed reactor effluent from the refrigeration cycle. 

Monomer Reactivity. The nature of the side chain R group exerts considerable influence on the reactivity of vinyl ethers toward cationic polymerization. The rate is fastest when the alkyl substituent is branched and electron-donating. Aromatic vinyl ethers are inherently less reactive and susceptible to side reactions. These observations are shown in Table 2. 

In laboratory preparations, sulfuric acid and hydrochloric acid have classically been used as esterification catalysts. However, formation of alkyl chlorides or dehydration, isomerization, or polymerization side reactions may result. Sulfonic acids, such as benzenesulfonic acid, toluenesulfonic acid, or methanesulfonic acid, are widely used in plant operations because of their less corrosive nature. Phosphoric acid is sometimes employed, but it leads to rather slow reactions. Soluble or supported metal salts minimize side reactions but usually require higher temperatures than strong acids. 

Thiadiazoloazines fused, 6, 711-748 alkyl side-chain activation, 6, 740 bond lengths, 6, 731 electrophilic reactions, 6, 735, 736 H NMR, 6, 731 IR spectra, 6, 732 mass spectra, 6, 732... 

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