Haloforms compounds

Carbene Reactions. The best procedure for preparing dihalocarbene adducts of olefins consists in stirring a haloform—methylene chloride solution with an excess of concentrated aqueous caustic soda in the presence of hen 2y1triethy1 amm onium chloride. Even stericahy hindered and electronically deactivated compounds give excellent yields (32). Mixed dihalocarbenes, CXY (X,Y = E, Cl, Br, I), except for CE2, can be prepared. 

In addition to the applications indicated on p. 858. hypohalous acids are useful halogenating agents for Ixjth aromatic and aliphatic compounds. HOBr and HOI are usually generated in silii. The ease of aromatic halogenation increa.ses in the sequence OCl < OBr < Ol and is facilitated by salts of Pb or Ag. Another well-known reaction of hypohalites is their cleavage of methyl ketones to form carboxylates and haloform ... 

Besides its synthetic importance, the haloform reaction is also used to test for the presence of a methylketone function or a methylcarbinol function in a molecule. Such compounds will upon treatment with iodine and an alkali... 

More useful for synthetic purposes, however, is the combination of the zinc-copper couple with methylene iodide to generate carbene-zinc iodide complex, which undergoes addition to double bonds exclusively to form cyclopropanes (7). The base-catalyzed generation of halocarbenes from haloforms (2) also provides a general route to 1,1-dihalocyclopropanes via carbene addition, as does the nonbasic generation of dihalocarbenes from phenyl(trihalomethyl)mercury compounds. Details of these reactions are given below. 

Our recent studies on effective bromination and oxidation using benzyltrimethylammonium tribromide (BTMA Br3), stable solid, are described. Those involve electrophilic bromination of aromatic compounds such as phenols, aromatic amines, aromatic ethers, acetanilides, arenes, and thiophene, a-bromination of arenes and acetophenones, and also bromo-addition to alkenes by the use of BTMA Br3. Furthermore, oxidation of alcohols, ethers, 1,4-benzenediols, hindered phenols, primary amines, hydrazo compounds, sulfides, and thiols, haloform reaction of methylketones, N-bromination of amides, Hofmann degradation of amides, and preparation of acylureas and carbamates by the use of BTMA Br3 are also presented. 

Any compound that oxidizes to a methyl ketone also gives a haloform reaction, because halogens are also oxidizing agents. For example, the compound shown in Figure 11-8 reacts. 

Ij can also oxidize 1° and 2° alcohols to carbonyl compounds. Which butyl alcohols give a positive haloform test ... 

Often compounds of CH2X2 type are called methylene halides, e.g. methylene chloride (CH2CI2), CHX3 type compounds are called haloforms, e.g. chloroform (CHCI3), and CX4 type compounds are called carbon tetrahalides, e.g. carbon tetrachloride (CCI4). Methylene chloride (dichlor-omethane, DCM), chloroform and carbon tetrachloride are extensively used in organic synthesis as nonpolar solvents. 

Of the disubstituted tetrahydronaphthalenes (V and VI), only Vic is a new compound, but Va was prepared by a new process. Furthermore, we had completed our synthesis of Vb before the appearance of the almost identical preparation of O Fabrell et al. [3] The hydroxyketone VI6 was prepared by the general method of O Farrell et al. [3], but our synthesis proceeded in much higher yield. Some unique results also have been obtained by subjecting 3-methoxy-5,6,7,8-tetrahydro-2-aeetonaphthone to the haloform reaction. 

Hydrolytic fission of a carbon chain which occurs with a,a,a-trihalo carbonyl compounds and which affords haloforms is observed with certain fluorinated compounds. Although R3C —F bonds are not broken, it is convenient to mention the process here. A special example is the hydrolysis of hexafluoro-2-phenylpropan-2-ol (5) in which two moles of trifluoromethane are liberated. 73... 

In spite of these difficulties with DOM chemistry, environmental chemists are frequently asked what molecular structures within the mixture are responsible for contaminant binding, haloform production, light attenuation, protonation characteristics, and other problems of environmental relevance. The chemist usually hypothesizes that DOM features such as aromaticity, polarity, functional-group content and configuration, molecular interactions, and molecular size can explain the observed phenomena. However, models of DOM (or DOM-fraction) structures must be based on average-mixture analyses to support these hypotheses. Such models represent average properties of thousands to millions of mixed compounds. 

There has been a growing interest in applying high performance liquid chromatography, to the determination of the not only volatile compounds, such as aliphatic and polyaromatic hydrocarbons, saturated and unsaturated aliphatic and polyaromatic hydrocarbons, saturated and unsaturated aliphatic halogen compounds, haloforms and some esters, phenols and others but also non volatile components of water. 

Other applications of gas chromatography to the determination of haloforms and aliphatic halogen compounds in non saline waters are discussed in Table 15.9. 

Gas chromatography has been applied to the determination of a wide range of organic compounds in trade effluents including the following types of compounds which are reviewed in Table 15.15 aromatic hydrocarbons, carboxylic acids aldehydes, non ionic surfactants (alkyl ethoxylated type) phenols monosaccharides chlorinated aliphatics and haloforms polychlorobiphenyls chlorlignosulphonates aliphatic and aromatic amines benzidine chloroanilines chloronitroanilines nitrocompounds nitrosamines dimethylformamide diethanolamine nitriloacetic acid pyridine pyridazinones substituted pyrrolidones alkyl hydantoins alkyl sulphides dialkyl suphides dithiocaibamate insecticides triazine herbicides and miscellaneous organic compounds. 

Volatile organic compounds inch aromatics haloforms and chloroaromatics... 

To determine the contribution of solvent to the proton shifts of halogen-substituted compounds, the shifts of haloformic protons (CHC13, CHBr3 and CHI3) have been measured in 24 -electron donor solvents1. The effect of hydrogen bonding on the proton shift... 

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