Bromoform CHBr

Removal of Refractory Organics. Ozone reacts slowly or insignificantly with certain micropoUutants in some source waters such as carbon tetrachloride, trichlorethylene (TCE), and perchlorethylene (PCE), as well as in chlorinated waters, ie, ttihalomethanes, THMs (eg, chloroform and bromoform), and haloacetic acids (HAAs) (eg, trichloroacetic acid). Some removal of these compounds occurs in the ozone contactor as a result of volatilization (115). Air-stripping in a packed column is effective for removing some THMs, but not CHBr. THMs can be adsorbed on granular activated carbon (GAG) but the adsorption efficiency is low. 

Condensation of vinyl chloride with formaldehyde and HCl (Prins reaction) yields 3,3-dichloro-l-propanol [83682-72-8] and 2,3-dichloro-l-propanol [616-23-9]. The 1,1-addition of chloroform [67-66-3] as well as the addition of other polyhalogen compounds to vinyl chloride are cataly2ed by transition-metal complexes (58). In the presence of iron pentacarbonyl [13463-40-6] both bromoform [75-25-2] CHBr, and iodoform [75-47-8] CHl, add to vinyl chloride (59,60). Other useful products of vinyl chloride addition reactions include 2,2-di luoro-4-chloro-l,3-dioxolane [162970-83-4] (61), 2-chloro-l-propanol [78-89-7] (62), 2-chloropropionaldehyde [683-50-1] (63), 4-nitrophenyl-p,p-dichloroethyl ketone [31689-13-1] (64), and p,p-dichloroethyl phenyl sulfone [3123-10-2] (65). 

At 225—275°C, bromination of the vapor yields bromochloromethanes CCl Br, CCl2Br2, and CClBr. Chloroform reacts with aluminum bromide to form bromoform, CHBr. Chloroform cannot be direcdy fluorinated with elementary flourine fluoroform, CHF, is produced from chloroform by reaction with hydrogen fluoride in the presence of a metallic fluoride catalyst (8). It is also a coproduct of monochlorodifluoromethane from the HF—CHCl reaction over antimony chlorofluoride. Iodine gives a characteristic purple solution in chloroform but does not react even at the boiling point. Iodoform, CHI, may be produced from chloroform by reaction with ethyl iodide in the presence of aluminum chloride however, this is not the route normally used for its preparation. 

Pecher et al. (2002) show how the uptake of ferrous iron from aqueous solution, by iron oxides, leads to the formation of a variety of reactive surface species that are capable of reducing polyhalogenated methanes (PHMs). The iron oxides used in the experiments and their characteristics are shown in Table 16.2. The PHMs studied include bromodichloromethane (CHBrCl ), chlorodibromomethane (CHBr Cl), bromoform (CHBr ), tetrachloromethane (CCl ), hexachloroethane (HCE), fluorotribromomethane (CFBrj), bromotrichloromethane (CBrCl ) and dibromodichloromethane (CBr Cy. 

When a base is used with a methy] ketone, the alpha carbon will become completely halogenated. This trihalo product reacts further with the base to produce a carboxylic acid and a haloform (chloroform, CHCI j bromoform, CHBr, or iodoform, CHIj). This is called the Haloform Reaction. 

Which would have the higher boiling point chloroform, CHCI3, or bromoform, CHBrs ... 

The formation of the bromomethanes CHBr and CH2Br2 by marine organisms is believed to be an enzymatic bromination of ketone metabolites (38, 39). A possible biosynthesis of bromoform and dibromomethane, postulated by Moore (38), is presented in Figure 7.5. Dibromochloromethane and dichlorobromo-methane are possibly directly produced by marine organisms or can also be formed by nucleophilic substitution of bromoform with chloride of sea water according to equations (3) and (4) (3, 23) ... 

Given that the pKa of tribromomethane, CHBrs (also known as bromoform) is 13.7, suggest what will happen when this ketone is treated with sodium hydroxide. 

PROBLEM 13.3 The NMR signal for bromoform (CHBra) appears at 2065 Hz when recorded on a 300-MHz NMR spectrometer, (a) What is the chemical shift of this proton (b) Is the proton in CHBrs more shielded or less shielded than the proton in CHCI3 ... 

This carbanion is capable of leaving because its negative charge is stabilized by the combined inductive effects of the three halogen atoms. It is still a moderately strong base with a pA., in the mid-teens. Proton transfer between this anion and the carboxylic acid gives the final products of the reaction, the salt of the acid and the haloform. bromoform (CHBrs). The same process occurs with trichloro- and triiodo-substituted methyl ketones, to give chloroform and iodoform, respectively. 

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