Potassium reaction + halogens

When pyrrole is treated with potassium (but not with sodium) or boiled with solid potassium hydroxide, potassium pyrrole C4H4NK is formed, which is the starting point for AT-deriva lives of pyrrole, since reaction of the potassium with halogen of organic compound and with carbon... 

Even in its more complex form, collision theory does not accurately predict the reaction between metal atoms such as sodium or potassium and halogen molecules such as bromine, for example K(g) + Brjfg) KBr(g) + Br(g). As the alkali metal atom approaches the bromine molecule its valence electron moves to the bromine molecule (thus providing a harpoon ). There are then two ions with an electrostatic attraction between them. As a result the ions move together and the reaction takes place. This mechanism, which has been worked out quantitatively, explains why the reaction occurs far more readily than might be expected taking into account only mechanical collisions between the alkali metal atoms and halogen molecules. 

Strictly speaking the alkyl halides are esters of the halogen acids, but since they enter into many reactions (t.g., formation of Grignard reagents, reaction with potassium cyanide to yield nitriles, etc.) which cannot be brought about by the other eaters, the alkyl halides are usually distinguished from the esters of the other inorganic acids. The preparation of a number of these is described below. 

Preparation of phlorogluciaol or its monomethyl ether by reaction of a halogenated phenol with an alkaU metal hydroxide in an inert organic medium by means of a benzyne intermediate has been patented (142). For example, 4-chlororesorcinol reacts with excess potassium hydroxide under nitrogen in refluxing pseudocumene (1,2,4-trimethylbenzene) with the consequent formation of pure phlorogluciaol in 68% yield. In a version of this process, the solvent is omitted but a small amount of water is employed (143). 

Various sulfides of the halogens are formed by direct combination of sulfur with fluorine, bromine, and chlorine. No evident reaction occurs with iodine instead, the elements remain as components of a mixture. Mixtures of sulfur and potassium chlorate, or sulfur and powdered zinc, are highly explosive. 

A number of compounds of the types RBiY2 or R2BiY, where Y is an anionic group other than halogen, have been prepared by the reaction of a dihalo- or halobismuthine with a lithium, sodium, potassium, ammonium, silver, or lead alkoxide (120,121), amide (122,123), a2ide (124,125), carboxylate (121,126), cyanide (125,127), dithiocarbamate (128,129), mercaptide (130,131), nitrate (108), phenoxide (120), selenocyanate (125), silanolate (132), thiocyanate (125,127), or xanthate (133). Dialkyl- and diaryUialobismuthines can also be readily converted to secondary bismuthides by treatment with an alkali metal (50,105,134) ... 

Furan reacts vigorously with chlorine and bromine at room temperature to give poly-halogenated products. Low temperature (-40 °C) reaction of furan with chlorine in dichloromethane yields mainly 2-chlorofuran and reaction of furan with dioxane dibromide at 0 °C affords 2-bromofuran in good yield. 2-Iodofuran is obtained by treatment of 2-furoic acid with iodine and potassium iodide in aqueous sodium hydroxide. 

Polymer-supported tetraphenylphosphonium bromide is a recyclable catalyst for halogen-exchange reactions. The reaction of 1 equivalent of chloro-2,4-dinitrobenzene with 1 5 equivalents of spray-dned potassium fluoride and 0.1 equivalent of this catalyst in acetonitnle at 80 C for 12 h gives 2,4-dinitro-fluorobenzene m 98% yield An 11% yield is obtained without the catalyst [3 /]. 

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