Alkyl benzenes synthesis

Methods of synthesis for carboxylic acids include (1) oxidation of alkyl-benzenes, (2) oxidative cleavage of alkenes, (3) oxidation of primary alcohols or aldehydes, (4) hydrolysis of nitriles, and (5) reaction of Grignard reagents with CO2 (carboxylation). General reactions of carboxylic acids include (1) loss of the acidic proton, (2) nucleophilic acyl substitution at the carbonyl group, (3) substitution on the a carbon, and (4) reduction. 

Based on petrochemicals, linear alkyl benzene sulfonates (LAS) are the most important surfactants. First description can be found in patents from the mid-1930s [2] using Fischer-Tropsch synthesis and Friedel-Crafts reactions. With the beginning of the 1950s the importance of the class of surfactants rose. The main use is in household and cleaning products. 

Figure 4.6. General scheme for the synthesis of linear alkyl benzenes, precursors to surfactants. Control over pore size of the catalyst can suppress the second alkylation almost completely. Given the ease with which the pore size can be chosen, one can design an effective catalyst for any particular reaction, and allow the selective and clean production of the desired mono-alkyl product, thus eliminating much of the waste associated with the process.

Although the ability of microwaves (MW) to heat water and other polar materials has been known for half a century or more, it was not until 1986 that two groups of researchers independently reported the application of MW heating to organic synthesis. Gedye et al. [1] found that several organic reactions in polar solvents could be performed rapidly and conveniently in closed Teflon vessels in a domestic MW oven. These reactions included the hydrolysis of amides and esters to carboxylic acids, esterification of carboxylic acids with alcohols, oxidation of alkyl benzenes to aromatic carboxylic acids and the conversion of alkyl halides to ethers. 

Dichiarante, V., Fagnoni, M. and Albini, A. (2007) Metal-free synthesis of sterically crowded biphenyl by direct Ar-H substitution in alkyl benzenes. Angewandte Chemie, International Edition, 46, 6495-6498. 

Uses. Tetramethylene sulfone has high solvent power for aromatics and has been used extensively by Olah and co-workers for Friedel-Crafts type nitrations and for studies of the mechanism of nitronium tetrafluoroborate nitration of alkyl-benzenes and halobenzenes in homogeneous solution. It is a superior solvent for quaternization of tertiary amines with alkyl halides, since it has a high dielectric constant and does not enter into side reactions observed with nitrobenzene and dimethylformamide. For example in the synthesis of the acridizinium salt (3), Bradsher and Parham effected quaternization of (1) with benzyl bromide in tetramethylene sulfone at room temperature in excellent yield. Several other salts analagous to (2) were obtained in good yield and in crystalline form with use of tetramethylene sulfone, whereas with other solvents the products were colored... 

Wang, E. Li, C. Simulation of suspension catalytic distillation for the synthesis of linear alkyl benzene. Chin. J. Chem. Eng. 2003,11 (5), 520-525. 

Aryl cation chemistry was likewise successful in the synthesis of biaryls, a common structural component of many pharmaceutically and biologically active compounds. In this way, sterically crowded biphenyls were smoothly synthesized by a direct Ar-H substitution in alkyl benzenes. The desired coupling took place satisfactorily, forming various bulky biaryl compounds in yields greater than 50% (mostly >70%, see Scheme 2.12). ... 

The lowest cost (di)alkyl benzenes are by-products from linear monoalkylate manufacture used extensively in detergent manufacture. Synthesis is usually by a Friedel-Crafts-type reaction, either by reaction of the alkyl chloride and benzene with anhydrous aluminium chloride as catalyst, or by the catalysed reaction of the appropriate length a-olefin and benzene. 

As the long chain olefins produced in the low temperature FT synthesis are almost exclusively linear alpha olefins, they are ideal for producing easily biodegradable detergents. Cuts from the Cg to products are reacted with benzene to produce alkyl benzenes which are sulphonated to give the detergents. The paraffins in the feedstock pass through the process, are chlorinated and used as plasticisers. Linear olefins can also be hydrofor-mulated to yield linear aldehydes and alcohols. 

In Friedel-Crafts alkylation, benzene is reacted with alkyl chlorides in the presence of metal halides (AICI3, AlBrj) as catalysts. The catalyst serves as Lewis acid and increases the electrophilicity of the alkyl halide. Alkylation is important for the synthesis of alkyl substituted derivatives of benzene. But there is a possibility of rearrangement of the intermediates resulting in undesired products. For example, if primary halides are used in alkylation, they can rearrange to form secondary or tertiary carbocations which are more stable intermediates. This can result in multiple products. 

Synthesis of alkylaromatics. Alkylaromatics are widely used for production of styrene (ethylbenzene), phenol (isopropylbenzene), and long chain alkylated benzene for detergent intermediates. 

Organic residual components are the most worrying because of their toxicity. Some of these compounds are formed as by-products. Volatile organic compounds are determined by headspace GC, GC-MS. Intermediate products, such as sultones and sulfones, from sulfonation of olefin and alkyl-benzene, respectively, can be detected by LC. Unreacted products, like ethylene oxide from the synthesis of ethoxylated nonionic and anionic surfactants, are studied by GC benzyl chloride from the quaternization of tertiary amines and aliphatic amines from amidation reaction are determined by LC (Figure 5). 

The mechanism of each of the reactions in the synthesis of phenol from benzene and propene via cumene hydroperoxide requires some comment. The first reaction is a familiar one. The isopropyl cation generated by the reaction of propene with the acid (H3PO4) alkylates benzene in a typical Friedel-Crafts electrophilic aromatic substitution ... 

The synthesis of ethylbenzene from benzene and ethylene was discovered in 1879 by M.Balsohn, who introduced ethylene gas into a mixture of benzene and aluminum chloride, and with heating to 70 to 80 °C obtained ethylbenzene and higher alkylated benzenes. In 1891, ethylbenzene was found in the xylene fraction of coal tar. 

Representative Electrophilic Aromatic Substitution Reactions of Benzene 457 Mechanistic Principles of Electrophilic Aromatic Substitution 458 Nitration of Benzene 459 Sulfonation of Benzene 461 Halogenation of Benzene 462 Biosynthetic Halogenation 464 Friedel-Crafts Alkylation of Benzene Friedel-Crafts Acylation of Benzene Synthesis of Alkylbenzenes by Acylation-Reduction 469 Rate and Regioselectivity in Electrophilic Aromatic Substitution 470 Rate and Regioselectivity in the Nitration ofToluene 472... 

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