Halogenation in water

S< o Ni) caustic alkalis halogenated in water- (alkaline freedom from ... 

Although solutions containing the hypohalous acids are produced by dissolving the halogens in water, the process must be carried out at low temperature. Hypohalites are also produced when halogens react in basic solution. 

Thus for saturated solutions of the halogens in water at 25°C we have the results shown in Table 13-6. There is an appreciable concentration of hypochlorous acid in a saturated aqueous solution of chlorine, a smaller concentration of HOBr... 

The easiest preparation of aqueous solutions of the hypohalous acids is to dissolve the appropriate halogen in water (equation 112). 

The effect of alkali on the hydrolysis of halogens in water is to shift the equilibrium to the right in reaction 2 (page 134). In the case of chlorine, the reaction goes almost to completion. An excess of alkali... 

The table contains some surprises Since the reduction potentials of the halogens in water decreases monotonically from F2 to I2, most chemists would probably have expected the electron affinities decrease in order... 

Biffinger JC, Sun H, Nelson AP, DiMagno SG (2003) Differential substituent effects of P-halogens in water-soluble porphyrins. Org Biomol Chem l(4) 733-736... 

Colourless crystals m.p. I25°C, soluble in water and alcohol. In aqueous solution forms equilibrium with its lactones. Gluconic acid is made by the oxidation of glucose by halogens, by electrolysis, by various moulds or by bacteria of the Acetobacter groups. 

It is slightly soluble in water, giving a neutral solution. It is chemically unreactive and is not easily oxidised or reduced and at room temperature it does not react with hydrogen, halogens, ozone or alkali metals. However, it decomposes into its elements on heating, the decomposition being exothermic ... 

Halogens can act as ligands and are commonly found in complex ions the ability of fluorine to form stable complex ions with elements in high oxidation states has already been discussed (p. 316). However, the chlorides of silver, lead(Il) and mercury(l) are worthy of note. These chlorides are insoluble in water and used as a test for the metal, but all dissolve in concentrated hydrochloric acid when the complex chlorides are produced, i.e. [AgCl2] , [PbC ] and [Hg Clj]", in the latter case the mercury(I) chloride having also disproportionated. 

When an organic compound is heated with a mixture of zinc powder and sodium carbonate, the nitrogen and halogens are converted into sodium cyanide and sodium hahdes respectively, and the sulphur into zinc sulphide (insoluble in water). The sodium cyanide and sodium hahdes are extracted with water and detected as in Lassaigne s method, whilst the zinc sulphide in the residue is decomposed with dilute acid and the hydrogen sulphide is identified with sodium plumbite or lead acetate paper. The test for nitrogen is thus not affected by the presence of sulphur this constitutes an advantage of the method. 

Iodine is a bluish-black, lustrous solid, volatizing at ordinary temperatures into a blue-violet gas with an irritating odor it forms compounds with many elements, but is less active than the other halogens, which displace it from iodides. Iodine exhibits some metallic-like properties. It dissolves readily in chloroform, carbon tetrachloride, or carbon disulfide to form beautiful purple solutions. It is only slightly soluble in water. 

Halogenation of 2-aminothiazole and derivatives has been reported under a wide variety of experimental conditions in water (161, 405. 406) in aqueous acids (16. 172, 407, 408) in solvents such as chloroform (27. 172), carbon disulfide (162, 166. 320. 409). benzene (165), acetic acid (410-413, 1580). or hydrochloric acid (414) or in 20% sulfuric acid (415-417). 

The choice of the solvent also has a profound influence on the observed sonochemistry. The effect of vapor pressure has already been mentioned. Other Hquid properties, such as surface tension and viscosity, wiU alter the threshold of cavitation, but this is generaUy a minor concern. The chemical reactivity of the solvent is often much more important. No solvent is inert under the high temperature conditions of cavitation (50). One may minimize this problem, however, by using robust solvents that have low vapor pressures so as to minimize their concentration in the vapor phase of the cavitation event. Alternatively, one may wish to take advantage of such secondary reactions, for example, by using halocarbons for sonochemical halogenations. With ultrasonic irradiations in water, the observed aqueous sonochemistry is dominated by secondary reactions of OH- and H- formed from the sonolysis of water vapor in the cavitation zone (51—53). 

The tnhahdes of phosphoms usually are obtained by direct halogenation under controlled conditions, eg, in carbon disulfide solution in the case of the triiodide. Phosphoms trifluoride [7647-19-0] is best made by transhalogenation of PCl using AsF or Cap2. AH of the phosphoms tnhahdes are both Lewis bases and acids. The phosphoms tnhahdes rapidly hydroly2e in water and are volatile. Examination by electron diffraction has confirmed pyramidal stmctures for the gaseous tnhahde molecules (36). Physical properties and heat of formation of some phosphoms hahdes are hsted in Table 7. 

At temperatures near the critical temperature, many organic degradation reactions are rapid. Halogenated hydrocarbons loose the halogen in minutes at 375°C (38). At temperatures typical of nuclear steam generators (271°C (520°F)), the decomposition of amines to alcohols and acids is well known (39). The pressure limits for the treatment of boiler waters using organic polymers reflect the rate of decomposition. 

PMVEMA, supphed as a white, fluffy powder, is soluble in ketones, esters, pyridine, lactams, and aldehydes, and insoluble in aUphatic, aromatic, or halogenated hydrocarbons, as well as in ethyl ether and nitroparaffins. When the copolymer dissolves in water or alcohols, the anhydride group is cleaved, forming the polymers in free acid form or the half-esters of the corresponding alcohol, respectively. Table 7 illustrates the commercially available alternating copolymers and derivatives. 

Halogen donors are chemicals that release active chlorine or bromine when dissolved in water. After release, the halogen reaction is similar to that of chlorine or bromide from other sources. SoHd halogen donors commonly used in cooling water systems include l-bromo-3-chloro-5,5-dimethyIhydantoin, l,3-dichloro-5,5-dimethyIhydantoin, and sodium dichloroisocyanurate. 

---