Squaraine chemistry. Synthesis of bis(4-dimethylaminophenyl)squaraine from dialkyl squarates. Mechanism and scope of the synthesis

Abstract

The mechanism and the scope of the synthesis of bis(4-dialky1aminoaryl)squaraines from di-n-butyl squarate and N,N-dialkylanilines have been studied. Results show that water and acid are key factors of the synthesis, and these two factors have been optimized. Yields of squaraine are also found to be sensitive to the steric effect provided by the alkyl chain in dialkyl squarates as well as to the concentration of the aniline reagent used in the synthesis. Mechanistic results suggest that alkyl squarate is the precursor of the synthesis, and that squaraine is formed by diarylation of alkyl squarate with an N,N-dialkylaniline derivative. Under optimized conditions, a number of squaraines have been synthesized. Yields, which are comparable to those synthesized from squaric acid. are obtained. Product analysis with good material balance has been achieved, and results show that arylation and diarylation of the starting di-n-butyl squarate are major side reactions in the squaraine synthesis.KOCK-YEE LAW et F. COURT BAILEY. Can. J . Chem. 64, 2267 (1986) On a 6tudiC le mecanisme et la gCnCralite de la synthese des bis(dia1kylamino-4 aryl) squarai'nes i partir du squarate de di-n-butyle et des N.N-dialkylanilines. Les rksultats indiquent que l'eau et l'acide sont des facteurs dkterminants dans la synthese et on a optimise ces deux facteurs. On a aussi trouve que les rendements en squaraine sont sensibles aux effets stkriques des chaines alkyles des squarates dialkylCs ainsi qu'i la concentration de l'aniline utiliske dans la synthese. Les rksultats mecanistiques suggerent que le squarate d'alkyle est un prkcurseur dans la synthese et que la squarai'ne se forme par une diarylation du squarate d'alkyle par un dkrivk N.N-dialkylaniline. Utilisant des conditions optimiskes. on a synthCtisC un certain nombre de squaraines. On a obtenu des rendements qui sont comparables a ceux obtenus lors de la synthese a partir de l'acide squarique. En se basant sur les produits dCtectCs, on a obtenu une bonne balance des rCactifs, et les resultats dkmontrent que l'arylation et la diarylation du squarate de di-n-butyle de depart sont des reactions secondaires importantes dans la synthbse de la squarai'ne .

Organic photoconductive materials: recent trends and developments

“…147 Law and Bailey reported that squaraines could also be synthesized from dialkyl squarate and iV^V-dimethylaniline derivatives (ester route, Scheme II). 154 Although the synthetic efficiency and scope of this new route are similar to the acid route, xerographic measurements showed that squaraines synthesized by this procedure consistently exhibit better xerographic properties, namely lower dark decay and higher charge acceptances.155 It was concluded from a mechanistic study that, due to the change in reaction condition, the microcrystalline squaraine products from the ester route are smaller in particle size and have a different crystallographic orientation. This morphological change results in "purer" squaraine samples and improvements in xerographic properties.…”

The synthesis and non-linear optical properties of (N-alkylpyrrol-2-yl)squaraine derivatives. Part 1

“…3,4-Dihydroxycyclobut-3-ene-1,2-dione, commonly known as squaric acid, condenses with two molar equivalents of an electron rich aromatic compound, such as an aniline or phenol, 1 to form intensely coloured squaraine dyes. Bis(anilino)squaraines and bis(benzothiazolium)squaraines, in particular, have been studied for a whole range of photophysical applications.…”

New unsymmetrical squaraine dyes derived from imidazo[1,5-a]pyridine

“…Butylsquarate (3-butoxy-4-hydroxy-1,2-dioxocyclobut-3-ene) was proposed as the reactive intermediate [28,29], firstly reacting with one molecule of the (hetero)aromatic compound to give an intermediate semisquaraine that subsequently undergoes a second condensation with another molecule of the same (hetero)aromatic compound to yield the final squaraine dye. The success of the reaction depends primarily on the nucleophilicity of the (hetero)aromatic species [30,31].…”