Condensation with aromatic rings

A halogen atom directly attached to a benzene ring is usually unreactive, unless it is activated by the nature and position of certain other substituent groups. It has been show n by Ullmann, however, that halogen atoms normally of low reactivity will condense with aromatic amines in the presence of an alkali carbonate (to absorb the hydrogen halide formed) and a trace of copper powder or oxide to act as a catalyst. This reaction, known as the Ullmant Condensation, is frequently used to prepare substituted diphenylamines it is exemplified... 

The condensation of aromatic rings with aldehydes or ketones is called hydroxy-alkylation. The reaction can be used to prepare alcohols, though more often the alcohol initially produced reacts with another molecule of aromatic compound (11-12) to give diarylation. For this the reaction is quite useful, an example being the preparation of l,l,l-trichloro-2, 2-bis (p-Chlorophenyl) ethane (DDT) ... 

The perinone ring system is thus formed by condensation with aromatic o-di-amines. Reaction of o-phenylenediamine with the monoanhydride is typically achieved in glacial acetic acid at 120°C. A mixture of the cis and trans isomers evolves, which appear as mixed crystals ... 

The quaternary salts of selenium-nitrogen heterocycles are labile to nucleophiles and can be converted to other heterocyclic systems by ring expansion [82, 103], An example is conversion of 1,2,4-selenadiazolium trifluoromethane sulfonate (67) into 1,3,5-selenadiazine (68) (Scheme 17) [104], 2,3-Dimethyl-1-benzo-l, 3-selenazolium tetrafluoroborate is readily condensed with aromatic aldehydes to 2-styrylselenazole [105] or treated with sodium hydride to give 3-methyl-2-methylene-2,3 -dihydro-1 -benzo-1,3 -selenazole [106],... 

Other reactions leading to NH4 removal from soil solution besides microbial nitrogen assimilation, metal-ammine formation, or adsorption onto mineral surfaces, involve NH3 fixation by incorporating it as NH2 in aromatic rings of humic acids (quinone) followed with aromatic ring condensation. 

Many patents, especially from Agfa and Kodak, deal with the preparation of dyes for color photography by coupling with diazonium salts (Table III). Dyes have also been obtained by condensations with aromatic aldehydes these may be salts (e.g., 431)"" or neutral molecules (432,"" 433 ). Cyanine dyes containing a polymethine chain between the azapentalene ring and the aryl moiety are also known. "" "" ... 

The data from these studies support the hypothesis that asphaltenes, viewed structurally, contain condensed polynuclear aromatic ring systems bearing alkyl side chains. These systems carry alkyl and alicyclic systems with heteroelements (i.e., nitrogen, oxygen, and sulfur) scattered... 

The chain length of the polyketide intermediate increases by units of two carbon atoms to various lengths. Cyclization of intermediates occurs by one of two pathways. An intramolecular aldol condensation produces aromatic rings with one substitution pattern (Fig. 5.2) and an intramo-... 

ALICYCLIC RINGS CONDENSED WITH AROMATIC SYSTEMS... 

H-Chemical Shifts (6 in ppm relative to TMS) and Coupling Constants (J in Hz) in Alicyclic Rings Condensed with Aromatic Systems... 

In most organic semiconductors, the % conjugation is extended through a linear condensation of aromatic rings. On the other hand, 2-D ir-extension systems with It stacking structures, which have not been extensively developed, are expected to afford unusual nano or microribbons. However, their OFET performances are relatively low compared to other series. 

Cyclic thioureas containing six-membered rings condense with aromatic isothiocyanates in the presence of mercury bis(phenylacetylide), in a similar manner to that described previously (see p. 401) for 2-mercaptoimidazoline, to give, eventually, the methiodide (84). Thiazolo[3,2-a]pyrimidine-5,7-diones, on alcoholysis or aminolysis, give the corresponding 2-substituted thiazoles [SO R = C(0)CHsCOsAlk or C(0)CHaC(0)NHAlk]. 3 ... 

Bcnzo[b]selenoph is and thdr Benzo-fused Derivatives.— The oxo-derivative (511) is a key intermediate in the synthesis of benzo[b]selenophens. Through reduction with sodium borohydride the parent compound is obtained, while reaction with methyl magnesium iodide yields the 3-methyl derivative. Under Vilsmeier formylation conditions, (511) was transformed into 3-chloro-2-formylbenzo[b]selenophen, a useful compound for the fusion of further rings. Compound (511) can also be condensed with aromatic aldehydes to compounds (512), some of them with antibacterial... 

The most important reaction of the diazonium salts is the condensation with phenols or aromatic amines to form the intensely coloured azo compounds. The phenol or amine is called the secondary component, and the process of coupling with a diazonium salt is the basis of manufacture of all the azo dyestuffs. The entering azo group goes into the p-position of the benzene ring if this is free, otherwise it takes up the o-position, e.g. diazotized aniline coupled with phenol gives benzeneazophenol. When only half a molecular proportion of nitrous acid is used in the diazotization of an aromatic amine a diazo-amino compound is formed. 

As carbazoles, where a ring containing nitrogen is condensed with one or more aromatic rings, forming neutral compounds. 

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