Ketomethylene

Dissolve 1 g. of the ketomethylene compound and 1 1 g. or 2 2 g. of pure benzaldehyde (according as to whether the compound may be regarded as RCOCHjR or as RCHjCOCHjR ) in about 10 ml. of rectified (or methylated) spirit, add 0 5 ml. of 5.N -sodium hydroxide solution, shake and allow the mixture to stand for about an hour at room temperature. The benzylidene derivative usually crystallises out or will do so upon scratching the walls of the vessel with a glass rod. Filter off the solid, wash it with a little cold alcohol, and recrystallise it from absolute alcohol (or absolute industrial spirit). 

Merocyanines belong to the class of nonionic methine dyes combining two nuclei, one of which is a ketomethylene of acidic nature such as pyrazolone, rhodanine, oxazolone, thiohydantoin,. 

The linking methine cheiin includes an even number of methine groups (0,2,4). They are commonly named as derivatives of the ketomethylene ring, for example. 3-ethyl-5-(3-ethyl-4,5-diphenylthiazolin-2-ylidene)-rhodanine (5) and 4-[4- 3-methyl-4,5-diphenylthiazolin-2-ylidene)-2-butenylidene]-3-methyl-l-p-sulfophenyl-2-pvrazolin-5-one (6) (Scheme 4). 

Rhodacyanines possess two chromophoric systems. They are at the same time neutrocyanine derivatives, which involves position 5 of the ketomethylene, and methine cyanine, which involves position 2. Following lUPAC s standard nomenclature rules, structure 7 is named 3-ethyl-4-phenyl-2- 4-oxo-3-ethyl-5-[2-(3-ethy]-2,3-dihydro-benzo-l,3-thiazo-lylidene)ethylidene]-tetrahydro-l,3-thiazolylidene-methyl -1.3-thiazolium iodide (Scheme 5). It implies that the 4-phenyl thiazole ring having the... 

The nucleophilic carbon of ketomethylene compounds can react with anhydrobases of different species in a basic medium. This reaction presents a narrow similitude with -CHj attack. The resulting dye, neut-rodimethine cyanine either mesomethyl-substituted or not. varies with the nature of the anhydro base (Scheme 30) (53. 54). 

Aniiinovinyl derivatives condense with methyl or methylene reactive groups of heterocycloammonium or ketomethylene. and are useful intermediates in the syntheses of thiazolotnmethine cyanines and thiazolodimethine neulrocyanine. They are prepared according to the following methods ... 

Very few compounds of this type have been described and appear in the tables of ketomethylene, anilinovinyl bases, and semicyanines (Scheme 36). 

Two different access routes are used, whether the leaving group is carried on thiazolium derivatives such as anilinovinyl (method A), acetanilidovinyl (method B), formyl methylene, or thioformylmethylene or on the ketomethylene compound (method C). The use of acid anhydride together with pyridine has been patented (method E). 

The electronic structure of a trimethine asymmetrical cyanine, controls the attack of a ketomethylene (Scheme 54). There is a condensation of the nucleophilic carbon on the electrophilic central carbon atom of the methine chain, leading to a neutrodimethine cyanine and simultaneously elimination of the more basic nucleus. 

The easier elimination of pyridine compared to quinoline-4 may be related to the pK value of 4-methylthiazole, which is between those of lepidine and 2-picoline (25. 55). This reaction explains also why a neutrodimethine cyanine is obtained with such good yields when reacting together a quaternary salt, ketomethylene, and o-ester in a basic medium. As the reaction proceeds, the trimethine cyanine is attacked by the ketomethylene. The resulting 2-methyl quaternary salt is transformed into trimethine cyanine, consuming the totality of the ketomethylene (1, p. 512 661). The mesosubstituted neutrodimethine cyanine is practically pure. 

Two access routes are also used with the vinylog derivatives of previous compounds, for example, either 2-(4-anilinobutadienyl)thiazolium with a ketomethylene, or 4-(4-anilinobutadienylidene)ketomethylene with 2-methylthiazolium. 

Hexamethine neutrocyanines are obtained by heating 2-(6-acetanilido-l,3,5-hexatrienyl)-4-arylthiazolium with ketomethylene and sodium acetate in acetic anhydride (69). 

Two moles of /3-alkoxyaicene can condense on each other by means of their a- and /3-carbon atoms. The resulting intermediate reacts on the anhydrobase by elimination of a molecule of ethanol resulting in a neocyanine formation (Schemes 59 and 60). Both monoanilino and bis-anilino derivatives resulting from the condensation of dimethylform-amide have been isolated. They are capable of furnishing various condensations on either ketomethylene or another reactive nucleus (Scheme 61). 

Synthesis and Properties. Polyquinolines are formed by the step-growth polymerization of o-aminophenyl (aryl) ketone monomers and ketone monomers with alpha hydrogens (mosdy acetophenone derivatives). Both AA—BB and AB-type polyquinolines are known as well as a number of copolymers. Polyquinolines have often been prepared by the Friedlander reaction (88), which involves either an acid- or a base-catalyzed condensation of an (9-amino aromatic aldehyde or ketone with a ketomethylene compound, producing quinoline. Surveys of monomers and their syntheses and properties have beenpubhshed (89—91). 

The wide variety of ketomethylene and amino ketone monomers that could be synthesized, and the abiUty of the quinoline-forming reaction to generate high molar mass polymers under relatively mild conditions, allow the synthesis of a series of polyquinolines with a wide stmctural variety. Thus polyquinolines with a range of chain stiffness from a semirigid chain to rod-like macromolecules have been synthesized. Polyquinolines are most often prepared by solution polymerization of bis(i9-amino aryl ketone) and bis (ketomethylene) monomers, where R = H or C H, in y -cresol with di-y -cresyl phosphate at 135—140°C for a period of 24—48 h (92). 

According to the position of nitrogen, the leaving substituent may be brought either by ketomethylene (5-ethoxymethylene) (method A) reacting on an aminothiazolium or by an amino derivative of this ketomethylene reacting on a 2-methylthiazolium (method B) (Scheme 57). 

These dyes possess two independent chromophoric chains of even methine (neutro) and uneven methine (cyanine) fixed on a central ketomethylene nucleus. The methylene reactive group is first used for the neutrocyanine synthesis in position 5. the quaternization of which can ensure a subsequent polymethine synthesis in position 2 of a cationic dye by ordinary means (Scheme 58). As indicated, this quaternized neutrocyanine (37) may as well give another neutrocyanine. 

As a consequence of the alternative distribution of an even number (2n) 7r electrons on an odd number (2n 1) carbon atoms, centers of the methine chain susceptible to nucleophilic attack are effectively the even carbons atoms starting from nitrogen, as it has been proven experimentally (103), particularly with a ketomethylene giving a neutrocyanine compound (53, 67). 

Cyanine Dyes Derived from ThiazoJium Salts TABLE 121. KETOMETHYLENE COMPOUNDS... 

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