Chlorination initiation

The diacid components for the manufacture of poly(y -phenyleneisophthalamide) and poly(p-phenyleneterephthalamide) are produced by one of two processes. In the first, the diacid chlorides are produced by the oxidation of / -xylene [108-38-3] or -xylene [106-42-3] followed by the reaction of the diacids with phosgene [75-44-5]. In the second, process m- or -xylene reacts with chlorine initiated by ultraviolet light to form the m- or Nhexachloroxylene. This then reacts with the respective aromatic dicarboxyUc acid to form the diacid chloride. 

Another common reaction is the chlorination of alkenes to give 1,2-dihaloalka-nes. Patell et al. reported that the addition of chlorine to ethene in acidic chloroalu-minate(III) ionic liquids gave 1,2-dichloroethane [68]. Under these conditions, the imidazole ring of imidazolium ionic liquid is chlorinated. Initially, the chlorination occurs at the 4- and 5-positions of the imidazole ring, and is followed by much slower chlorination at the 2-position. This does not affect the outcome of the alkene chlorination reaction and it was found that the chlorinated imidazolium ionic liquids are excellent catalysts for the reaction (Scheme 5.1-39). 

As an example, a mixture of hydroquinone and concentrated hydrochloric acid is chlorinated initially at 10°C. After adding water, the reaction mixture is heated and the chlorination continued. Similar but slightly modified routes involve using hydrochloric acid/H202 or chlorine/water. Hydroquinone may be replaced by ben-zoquinone [2],... 

Edney, E. O., B. W. Gay, and D. J. Driscoll, Chlorine Initiated Oxidation Studies of Hydrochlorofluorocarbons—Results for HCFC-123 (CF,CHCI2) and HCFC-141b (CFC12CH,), J. Atmos. Chem.., 12, 105-120 (1991). 

Volatile irritants such as ammonia and chlorine initially cause constriction of the bronchioles. These two gases are water soluble, are absorbed in the aqueous secretions of the upper airways of the respiratory system, and may not cause permanent damage. Irritant damage may however lead to changes in permeability and edema, the accumulation of fluid. Some irritants such as arsenic compounds cause bronchitis. 

Ramos DR, Garcia MV, Canle LM, Santaballa JA, Furtmiiller PG, Obinger C (2007) Myeloperoxidase-catalyzed taurine chlorination Initial versus equilibrium rate. Arch Bio-chem Biophys 466 221-233... 

Retrospective studies (see Table 4-3) of soldiers exposed to chlorine gas indicate that chlorine initially causes dyspnea, pulmonary edema, bronchitis, and pneumonia, which can result in death (Gilchrist and Matz 1933, as cited in Das and Blanc 1993 Meakins and Priestly 1919). Some subjects continued to suffer respiratory problems for years after exposure (Gilchrist and Matz 1933, as cited in Das and Blanc 1993). 

Figure 24. Autooscillations of rate of methylcyclohexane chlorination in its equimolar mix with molecular chlorine. Initial temperature is 45 K. Radical concentration created with prephotolysis is 4 X 10 cm"...

The chlorine-initiated reaction of CFj=CFCl with dioxygen in a flow system, in the dark at room temperature, gives predominantly CFjClC(0)F, COFj, and COCIF [1197]. The following reactions are indicated ... 

Petway, S. V. Application of Automatic Reaction Model Generation to Chlorine-Initiated Neopentane Oxidation, (Poster Presentation) 6th International Conference on Chemical Kinetics, NIST (Gaithersburg, MD) (2005). 

When about 1-3 per cent of an aliphatic halogenated compound or a nitro compound is added to a paraffin-olefin mixture, the alkylation reaction proceeds at milder temperatures, about 300-400°C. The substances that are effective have a relatively low thermal stability and form free radicals at the reaction temperatures. The free radicals react similarly to those of Eqs. (3) and (4). The products obtained contain some chlorine atoms when a chlorinated initiator is used otherwise the products are similar to those in which no initiators are used. 

Without absorption of further light energy, the atoms of chlorine initiate the chain reaction illustrated by reactions (8) and (9). Such chain reactions are fast but not necessarily explosive. They become explosive when the heat evolved in the overall reaction is so large that constant temperature cannot be maintained as the reaction proceeds, the heat evolved increases the temperature which, in turn, increases the rate of the reaction and the liberation of heat until, finally, the reaction becomes explosive. 

Studied the products of the chlorine-initiated oxidation of dimethyl carbonate in 700 Torr of N2/O2 diluent at 296 K. IR product features consistent with the formation of CH30C(0)0C(0)H were observed. The yield of CH30C(0)0C(0)H varied with [O2] in a manner consistent with competition between three reaction pathways for... 

Ohta, T., H. Bandow, and H. Akimoto (1982), Gas-phase chlorine-initiated photooxidation of methanol and isopropanol, Int. J. Chem. Kinet., 14, 173-182. 

Richter, H.R., J.R. Sodeau, and 1. Barnes (1993), The photolysis and chlorine-initiated photooxidation of trifluoroacetaldehyde, STEP-HALOLSIDE/AFEAS Workshop, Dublin, 23—25 March, pp.182—188. 

---