Chloranil reaction with amines

Reactions on or close to solid surfaces maybe inhibited by deposition ofinsoluble or poorly soluble products on the reactant surface, a phenomenon referred to as overgrowth. Examples include the reaction of amines with chloranil [7], the diazotisation of poorly soluble aromatic amines in which the product diazonium salt is also insoluble and halogen exchange reactions of chloroaromatic compounds using potassium fluoride in dipolar aprotic solvents where the potassium chloride product may coat the potassium fluoride [8]. 

As with chloranil, one should be aware of the possibility of a displacement reaction with TCNQ or TCNE (tetracyanoethylene). Indole has been observed to react with TCNE in solution at ordinary temperatures. A reaction with JV-alkylanilines is also observed. Amines have been observed to displace a cyano group from TCNE and TCNQ. Formation of these... 

Note It is reported that the use of chlorobenzene as solvent is essential when the reagent is to be used to detect aromatic amines [1]. In the case of steroids, penicillins, diuretics and alkaloids the reaction should be accelerated and intensified by spraying afterwards with dimethylsulfoxide (DMSO) or dimethylformamide (DMF), indeed this step makes it possible to detect some substances when this would not otherwise be possible [5,9-11] this latter treatment can, like heating, cause color changes [5,9]. Penicillins and diuretics only exhibit weak reactions if not treated afterwards with DMF [10, 11]. Steroids alone also yield colored derivatives with DMSO [9]. Tlreatment afterwards with diluted sulfuric acid (c = 2 mol/L) also leads to an improvement in detection sensitivity in the case of a range of alkaloids. In the case of pyrrolizidine alkaloids it is possible to use o-chloranil as an alternative detection reagent however, in this case it is recommended that the plate be treated afterwards with a solution of 2 g 4-(dimethyl-amino)-benzaldehyde and 2 ml boron trifluoride etherate in 100 ml anhydrous ethanol because otherwise the colors initially produced with o-chloranil rapidly fade [12]. 

AFM has been used in real time to image reacting surfaces in contact with a liquid phase [35]. A study ofthe self-passivating reactionbetween p-chloranil and an aromatic amine included monitoring the surface topography of the p-chloranil in contact with the amine in aqueous solution at 25-second intervals, Fig. 5.27. Under the conditions employed, passivation by the reaction product was shown to be complete in 5 minutes a concomitant hydroxide induced dissolution could also be monitored [7]. 

The presence of pending primary aromatic amine groups bound to a solid can be detected according to equation 21, by heating the solid with a DMF solution of chloranil (131). Development of color in the solid points to formation of dyes (132). A semiquan-titative comparimetric method can be developed for various resins based on this reaction. No interference was noted from secondary and tertiary aromatic amines, nor from pyridine and pyrimidine moieties241. 

The universally applicable dioxazine pigment, especially Pigment Violet 23, which is distinguished by good color strength, is commercially important. It is produced by the reaction of 3-amino-N-ethylcarbazole and chloranil in o-dichloro-benzene at temperatures between 130 and 150 °C followed by oxidative ring closure to the dioxazine in the presence of benzenesulfonyl chloride. The 3-amino-N-ethylcarbazole required for the synthesis is produced from carbazole by N-alkyla-tion, e.g. with diethyl sulfate or ethyl chloride, and nitration followed by the reduction to the amine. 

With Fe2(CO)9 as catalyst, the CDC reaction of saturated heterocycles with 1,3-diketones was accomplished using TBP as an eflhcient oxidant (Scheme 2.12) [48]. This protocol shows good compatibility to cyclic and acyclic ethers, thioe-thers, and tertiary amines. Gratifyingly, besides C(sp )-C(sp ) coupling, the oxidative C-N coupling of ethers with azoles also works well (Scheme 2.12) [49]. As a update, with 2-chloranil (tetrachloro-l,2-benzoquinone) as oxidant, benzyl thioethers can be employed as substrates under metal-free conditions [50]. Notably, 2,2,6,6-tetramethylpiperidine-l-oxoammonium tetrafluoro borate is also an effective oxidant for metal-free CDC reaction of isochromanes and carbonyl compounds [51, 52]. 

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