Friedel-Crafts self-condensation

HCP-l,4-benzenedimethanol (HCP-BDM) and HCP-ben l alcohol (HCP-BA) networks synthesized by the Friedel-Crafts self-condensation method have shown high selectivity for CO2 over N2, measured by nitrogen adsorption isotherm at two different temperatures, 273 and 298 Nonlocal density functional theory (NLDFT) calculations confirmed the pore sizes to be below 2 nm for both of the networks. Such small pore sizes, as well as the high ojq gen content in both the polymers, is most probably tbe reason for the strong interactions with polar CO2 rather than N2, making these good candidates for the selective separation of CO2 from N2. 

The earliest reported reference describing the synthesis of phenylene sulfide stmctures is that of Friedel and Crafts in 1888 (6). The electrophilic reactions studied were based on reactions of benzene and various sulfur sources. These electrophilic substitution reactions were characterized by low yields (50—80%) of rather poorly characterized products by the standards of 1990s. Products contained many by-products, such as thianthrene. Results of self-condensation of thiophenol, catalyzed by aluminum chloride and sulfuric acid (7), were analogous to those of Friedel and Crafts. 

As is the case during manufacture, contact with those metallic impurities that catalyze Friedel-Crafts condensation reactions must be avoided. The self-condensation reaction is exothermic and the reaction can accelerate producing a rapid buildup of hydrogen chloride pressure in closed systems. 

The molten material, after holding for 4 h at 78°C in a stainless steel vessel, underwent a thermal runaway reaction and 500 kg erupted through the vent line. It was later found that addition of 0.1% of rust to the hot material led to an accelerating self-condensation Friedel-Craft reaction, catalysed by iron(III) chloride, which led to formation of poly-benzyls accompanied by evolution of hydrogen chloride. 

As industrial relevant Friedel-Crafts reaction, the synthesis of Bisphenol-F, a material for epoxy resin, from phenol and formaldehyde was chosen [57]. This reaction involves formation of higher order condensates such as tris-phenols. To minimize the latter, the molar ratio of phenol to formaldehyde is set to a very high value (30-40), which is more than 15 times larger than the amount theoretically necessary. Three types of micromixers were used. These are a T-shaped mixer with 500 pm inner diameter, a multilaminating interdigital micromixer with 40 pm channels and a so-called self-made K-M micromixer with center collision mixing. 

Besides the addition of such reagents as halogens, hydrogen halides, or the hypohalous acids, there are other reactions which appear to proceed through addition mechanisms, but the exact course of the process is sometimes considerably obscured. The Friedel-Crafts addition of alkyl halides to olefins (p. 145), the self-condensation of olefins, and the alkylation of isoparaffins are examples in which attack at the double bond seems to be led by a carbonium ion. 

Fig. 5.5 Synthesis of HCP-BA by Friedel-Crafts catalyzed self-condensation (Reprinted with permission from Ref. [32]. Copyright 2013, Royal Society of Chemistry)...

Various synthetic approaches have been demonstrated for the synthesis of PAEs since early days [35 0], PAEs were synthesized by Ullmann condensation between bisphenols and aryl fcis-halide monomers using Cu(I) salt/pyridine as catalyst [36], General Electric developed the first commercially successful PAE poly(2,6-dimethyl phenylene oxide) (PPO) [38], It was prepared by oxidative coupling of 2,6-dimethyI phenol. However, this process has its own restrictions, because it does not allow much structural variation or inclusion of any electron-withdrawing group into the polymer main chain. First attempts to synthesize polysulfones (PSF) were successfully done by Friedel-Crafts sulfonylation reaction of arylenedisulfonyl chlorides, for example, diphenyl ether-4,4 -disulfonyl chloride with diaryl ethers, for example, diphenyl ether, or by self-condensation of 4-phenoxy benzene sulfonyl chloride in the presence of FeCls [41], Whereas the former reaction involves side reactions (sulfonylation not only in the para- but also in the ort/io-position), the latter produces only the desired linear all-para products. 

Tan et al. explored the synthesis of monomers that are monofunctional. They have synthesized two hypercrosslinked polymer networks of bishy-dro>ymethyl monomers, e.g., 1,4-benzenedimethanol (BDM), and mono-hydro>ymethyl compounds, e.g., benzyl alcohol (BA) by self-condensation. Precursors of polymers like polystyrene and poly(chloromethylstyrene) ° that are swollen, as well as polyfunctional benzyl chlorides, are synthesized by Friedel-Crafts allq lation in the presence of a Lewis acid. Hydroxymethyl and chloromethyl form a bond with the benzene ring in the presence of an acid catalyst,leading to the design of a new series of hypercrosslinked polymers prepared by directly using the building blocks of hydro)g7methyl aromatics (Figure 3.2). 

Figure 4.7 S3Tithesis of HCP-BDM and HCP-BA by a Friedel-Crafts reaction cata-l5 ed under self-condensation.

The self-condensation of sulfonoimidoyl chlorides such as A/ -tosyl (Ts) derivative of the benzene- and 4-phenoxybenzene-sulfonimidoyl chloride (142) utilizing a catalytic (AICI3 or FeCla) Friedel-Crafts reaction has been studied as a way to produce these polymers. It has been foimd that the reaction of the former compound yielded no polymeric product, whereas that of (142) produced exclusively methanol-insoluble polymer (143) of Mn = 14,500 with polydispersity = 1.45 in 80% yield (317). 

The self-condensation of furan-2-yl alcohols and subsequent intramolecular Friedel-Crafts-type reaction and elimination of an aldehyde catalyzed by ytterbium triflate gave rise to di(furan-2-yl) methanes, which are precursors for the synthesis of biofuels (130BC8030). 

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