Potassium reaction + halogen atoms

The nature of the leaving halogeno atom. It has been observed that reaction of mono-labeled 6-fluoro-, 6-chloro-, and 6-iodo-4-phenyl[l(3)- Njpyrimidine with potassium amide/liquid ammonia leads to 6-amino-4-phenylpyrimidine in which the exocyclic amino group is N-labeled the percentages, however, strongly depend on the nature of the halogen atom, i.e., F (73 5%), Cl (93 5%), Br (83 5%), I (13 5%) (Scheme 11.12) (72RTC1414). 

Carbenes are also formed by reactions of halogenated compounds with bases. If a carbon atom has bonds to at least one hydrogen and to enough halogen atoms to make the hydrogen slightly acidic, it may be possible to form a carbene. For example, bro-moform (CHBr3) reacts with a 50% aqueous solution of potassium hydroxide to form dibromocarbene. 

The formation of cyano ketones by this method is illustrated by the conversion of phenacyl halides to the corresponding nitriles. Ring closure to cyclopropane derivatives is a side reaction which has been encountered with y-halo ketones. Benzalacetophenone dibromide is converted by alcoholic potassium cyanide to the fi-cyaao ketone, the a-halogen atom being reduced. Several a-chloro ketones have been found to yield a-cyano epoxides. ... 

The application of chemiluminescence by Polanyi and his collaborators to the determination of the dissociation energies of sodium and potassium is an elegant but rather specialized study in the field. It was found that when sodium and halogen vapours react in a very dilute flame , intense chemiluminescence is produced, which can only be attributed to the reaction of halogen atoms with Na2 molecules ... 

Many cyclopropyl chlorides and bromides have been converted to alkoxycyclopropanes by treatment with a strong base, in most cases potassium rerf-butoxide, in an appropriate organic solvent (Table 13). Under such conditions, hydrogen halide elimination takes place, yielding strained cyclopropene intermediates, which are trapped by nucleophilic attack of the alkoxide. Overall, a simple substitution occurs when a bond is formed between the alkoxide group and the carbon atom to which the halide was attached. This is the case when l-chloro-5-methyl-exo-6-phenyl-3-oxabicyclo[3.1.0]hexan-2-one (1) was reacted with potassium /ert-butoxide l-/er/-butoxy-5-methyl-ent/o-6-phenyl-3-oxabicyclo[3.1.0]hexan-2-one (2) was isolated in 94% yield.If a C-O bond is established at the other olefinic carbon atom, a C H bond is concomitantly formed at the carbon atom, to which the halide was attached. The result is a double substitution which is discussed elsewhere (see Section 5.2.1.3 ). When the substrate contains more than one halogen atom, several elimination reactions usually take place. Thus, treatment of 1 -bromo-2-chloro-2-methylcyclopropane (3) with an excess of potassium /er/-butoxide gave l-ter/-butoxy-2-methylenecyclopropane (4) in 30% yield. 

When halocyclopropanes react with an alkali metal alkoxide in an organic solvent, elimination-addition reactions take place and result in formation of alkoxycyclopropanes. In most cases the overall reaction can be regarded as a simple substitution of a halogen atom by an alkoxy group (see Section 5.2.1.1.11.2.2.), but in some cases a double substitution is observed. The latter reaction occurred when 6,6-dichloro-3-thiabicyclo[3.1.0]hexane was treated with potassium fcr/-butoxide and gave l-tcrt-butoxy-e r/o-6-chloro-3-thiabicyclo[3.1.0]hexane (1) in 68% yield. The reaction is believed to take place via a strained cyclopropene intermediate, which is trapped by nucleophilic attack of the ferr-butoxide or by reaction with furan if present.Other 1,1-dichlorocyclopropanes react analogously under similar conditions, 22-724 jjyj jien an excess of base is used, a second elimination-addition... 

It has to be clearly understood, however, that the electronic excitation and the formation of the metal and halogen atoms are different processes. Thus temperature, which has little effect on the ultra-violet absorption spectrum of potassium bromide in a wider range (100-400°C) has a marked influence on the quantum efficiency of the reaction forming colour centres31 32. Thus at — 100°C no metal atoms are formed whereas at 400°C almost every quantum absorbed gives rise to a metal atom. The quantum efficiency at 0°C is J. This implies that the production of metal atoms is a secondary process, dependent on the thermal oscillations of the crystal lattice, which, however, has little or no effect on the primary process of electron excitation on absorption of light quanta. The reaction may therefore be represented as follows for the alkali halide, MX. 

Selected data on metathetical reactions of sodium and potassium atoms transfer of halogen atoms... 

Emission from electronically excited TiO molecules has been observed by Palmer and co-workers from the reaction of titanium tetrachloride or tetrabromide with potassium vapour in the presence of oxygen [277] and of nitrous oxide [278]. The potassium atoms presumably strip the halogen atoms from the titanium tetrahalide, and the titanium atoms then react with the oxygen or nitrous oxide producing electronically excited TiO molecules. 

It should be noted that these reactions are analogous to those which take place between alkyl halides and water and alkalies. The effect of the presence of two halogen atoms is to make it possible for the reactions to take place much more rapidly and at a lower temperature. Other reactions in which ethylene bromide resembles the alkyl halides are those which take place with ammonia and potassium cyanide... 

The chemical properties of the three isomers illustrate the effect of the relative position of substituents on their activity. o-Nitrobromobenzene (m.p. 43°) is converted into o-nitroaniline when heated at 190° with an alcoholic solution of ammonia, and into o-bromophenol when heated at a high temperature with water and potassium hydroxide. In one reaction the halogen atom is removed by ammonia, and in the other the nitro group by potassium hydroxide. p-Nitrobromobenzene enters into similar reactions, but the meta compound is not affected by the... 

Dihydroxyacetone (44) was conveniently prepared from halogenopropargyl alcohol (43) by hydration of the triple bond followed by substitution of a halogen atom for the OH group in a reaction with potassium formate. DL-Erythrulose was obtained from 2-butyne-l,4-diol (45) in an improved way involving conversion to 1-acetoxy-3-buten-2-one (46), formation of the bromohydrin (47), substitution of the bromine atom for an OAc group in a reaction with silver acetate, and final deacetylation. 

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