Replacement by halogen with

The recurring theme in work on corticoids discussed thus far with the exception of the 17-desoxy compounds consisted in the introduction of additional functions to the basic cortisone molecule. Some further success in producing biologically active molecules has been achieved by substituting unnatural functions for those present in the protoype molecule. Thus the hydroxyl groups at both C-ll and C-21 can be replaced by halogen with retention of activity. 

There have been several further examples of the replacement of hydroxyl or oxo substituents with halogens in 1,7-phenanthrolines using phosphorus halides or oxyhalides. " In 4,10-dioxo-l,4,7,10-tetrahydro-l,7-phenanthroline (100) there are marked differences in the ease with which the two oxo groups are replaced by halogen. With 1 mole of phosphorus pentachloride, the product is 4-chloro-lO-hydroxy-... 

There are three compounds with the formula C6H4ClBr in which two of the hydrogen atoms of the benzene molecule have been replaced by halogen atoms. Draw structures for these compounds. 

The ring strain inherent in species XV increases its propensity for polymerization. A substantial number of organo-halogenocyclophosphazenes have now been polymerized (7-17). After polymerization, the halogen atoms can be replaced by treatment with alkoxides, aryloxides, primary or secondary amines, or organometallic reagents. 

Aromatic amination by replacement of halogens with amines (example... 

In very reactive halogen derivatives such as a-bromo ketones [234] and a-bromothiophene [235] the halogens are replaced by hydrogen with hydrogen bromide in acetic acid provided phenol is added to react with the evolved bromine and to affect favorably the equilibrium of the reversible reaction. Hydrogen bromide in acetic acid also reduces azides to amines [232],... 

The cluster [Mo4(pt3-S)2(M2-S)4(SH)2(PMe3)6] has been prepared by the reaction of (NH4)2[Mo3S13] with trimethylphosphine in a mixed solvent of butylamine and thf at room temperature followed by reflux in 14% yield (99). The SH ligands can be replaced by halogens in reac-... 

The reason why boiling points of completely shielded compounds rise if the halogens are replaced by others with a higher atomic number will be dealt with later in Section 51. 

Several further examples have been reported of the replacement of hydroxyl (or oxo) substituents in 1,10-phenanthrolines by halogens with phosphorus halide reagents.38 96 196,198,213 213,219,293,340-342 4-Ethoxy-7-hydroxy-l,10-phenanthroline reacts normally with diazomethane to afford 4-ethoxy-7-methoxy-1,10-phenanthroline.203... 

The oxygen of ketone and aldehyde groups is readily replaced by halogen under the influence of phosphorus trichloride or pentachloride the reaction may be carried out with or without a solvent solvents commonly employed are chloroform, benzene, petroleum ether, acetyl chloride and phosphorus oxychloride. 

The hydroxyl group of the side-chain alcohols is readily replaced by halogen by treatment with thionyl chloride 87,190,336,486,526-528,529 or by treatment with phosphorus tribromide in chloroform193 439 447-... 

Polysilanes have also been modified by removal of aryl groups under acidic conditions, to give Si-functional polymers. Phenyl or other aryl groups on silicon can be selectively replaced by halogens, upon treatment with a hydrogen halide and a Lewis acid. 

Alkanes are fuels they burn in air if ignited. Complete combustion gives carbon dioxide and water less complete combustion gives carbon monoxide or other less oxidized forms of carbon. Alkanes react with halogens (chlorine or bromine) in a reaction initiated by heat or light. One or more hydrogens can be replaced by halogens. This substitution reaction occurs by a free-radical chain mechanism. 

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