Methoxybiphenyls, oxidation

Poly(epichlorohydrin) (PECH) and poly(2,6 - dimethyl-1,4-phenylene oxide) (PPO) containing pendant mesogenic units separated form the main chain through spacers of zero to ten methylene units were synthesized and characterized in order to test the "spacer concept." Both polymers were modified by phase transfer catalyzed esterifications of the chloromethyl groups (PECH) or the bromobenzyl groups (brominated PPO) with potassium co -(4-oxybiphenyl) alkanoates and potassium u-(4-methoxy-4-oxybiphenyl)-alk.an oates. While PPO required ten methylene units as a spacer and 4,4 -methoxybiphenyl as mesogen to present thermotropic liquid crystalline mesomorphism,... 

Several other organic systems have been stndied as potential electrochromes because of their redox behaviour. These include carbazoles, methoxybiphenyls, fluorenones, benzoquinones, naphthaquinones and anthraqninones, tetracyanoquinodimethane, tetrathiafnlvalene and pyrazolines. ° Of particnlar interest are the 1,4-phenylenedi-amines, which form highly colonred species on oxidation. These, known as Wurster s salts, exemplified by Wnrster s Bine (1.97), are anodically colouring and this type of material has found nse in composite electrochromic systems for car rearview mirrors (see 1.5.4.1). 

The reaction of n radical cations with n nucleophiles usually leads to C-C bond formation, a reaction that can be very fast (cf. pericyclic reactions also), as in the oxidative dimerization of triphenylamine k = 1-10 x 10 M s ) [293], Hence, such a reaction mechanism can even operate in anodic oxidations (4-methoxybiphenyl [294], tetrahydrocarbazole [295], 4,4 -dimethoxystilbene [296] and 9-methoxyanthracene) [297], where the radical cation concentration is very high. 

In acetonitrile, methoxybiphenyls are coupled in low yield, but almost quantitatively in dichloromethane-trifluoroacetic acid [135,136]. Yields are low in the first solvent because the cyclized products are more easily oxidized than their precursors and the oxidation products are not stable. In the presence of TEA, the cation radicals derived from the oxidation of cyclized XXII are stable and after reduction with zinc dust, for example, cyclized XXII may be isolated in high yield. 

The Stille reactions of aryl chlorides, as the least reactive electrophilic substrates can be successfully performed by applying a palladium-complex of electron-rich and sterically encumbered Pt-Bus as Pd(0)-stabilizing ligand [78]. The latter increases the electron-density at palladium metallic centre and thus facilitates the oxidative addition step of unreactive electron-rich aryl chlorides to the Pd(Pt-Bu3)2- For instance, even 4-chloroanisole (76), among the least reactive chlorides, was reacted with phenyltri-n-butylstannane (184) to give 4-methoxybiphenyl (78) in 94% yield [78], respectively,... 

From one to four units of ethylene oxide have been used to space a group with liquid crystalline properties, methoxybiphenyl, different distances from a methacrylate group (34). Hydrodynamic and thermodynamic properties were calculated. 

P[ly(methoxy-biphenyl methaciylate-co-methoxybiphenyl ethylene oxide methaciylate) p THF HI aw... 

Poly(methoxybiphenyl methaciylate-co-methoxybiphenyl lris(ethylene oxide)methacrylate)... 

Poly(methoxybiphenyl tiis(ethylene oxide)methaciylate)... 

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