Decarboxylative dechlorination

The preceding deactivation processes are generally considered to be photophysical processes. In addition to these, deactivation can take place via photochemical processes such as photoionization, decarboxylation, dechlorination, and permanent product formation. All these processes can be studied under steady-state or time-resolved domains. 

LePree tested eq. [5.5.49] with the decarboxylative dechlorination ofN-chloroamino... 

ETHYL BENZOATE VIA THE NITRO-SOAMIDE DECOMPOSITION, 47, 44 Decachlorobi-2,4-cyclopentadienyl, dechlorination by triisopropyl phosphite, 46, 93 a-Decalones, 46, 82 Decanoyl fluoride, 46, 6 Decarboxylation, in formation of couma-rone from o-formylphenoxyacetic acid, 46, 28... 

Decarboxylation reactions 26 Dechlorination 277 DHPMs 34 Diazepines 259 Diazines 242... 

Photodecomposition products included acidic compounds and five methylated derivatives (Plimmer, 1970). When picloram in an aqueous solution (25 °C) was exposed by a high intensity monochromatic UV lamp, dechlorination occurred yielding 4-amino-3,5-dichloro-6-hydroxy-picolinic acid which underwent decarboxylation to give 4-amino-3,5-dichloropyridin-2-ol. In addition, decarboxylation of picloram yielded 2,3,5-trichloro-4-pyridylamine which may undergo dechlorination yielding 4-amino-3,5-dichloro-6-hydroxypicolinic acid (Burkhard and Guth, 1979). 

Tetrafluoroethylene is a colorless, odorless gas which boils at —76.3° C at atmospheric pressure and freezes at —142.5° C (Renfrew and Lewis). Its critical temperature and pressure are 33.3° C and 572 psi. The heat of formation is —151.9 kcal/mole, (Duus Bryant Neugebauer and Margrave), and the heat of polymerization is —41.12 kcal/mole (Bryant). The first reliable report of the preparation of this compound was in 1933 by Ruff and Bretschneider, who decomposed tetrafluoromethane in an electric arc. Other syntheses are based on the dechlorination of sym-dichlorotetrafluoroethane (Locke, Brode, and Henne), the pyrolysis of difluorochloromethane (Downing, Benning, and McHarness Tor-kington and Thompson) or the decarboxylation of sodium perfluoro-proprionate (Hals, Reid, and Smith). 

Unsubstituted 2,7-naphthyridine (50) is probably best made by oxidation of 2,7-naphthyridine-4-carbaldehyde to 2,7-naphthyridine-4-carboxylic acid (49) (KMn04, AcMe, 20°C 88%) and subsequent thermal decarboxylation (Cu powder, gentle heat 78%) 630 earlier syntheses involved direct hydrogenolysis of 1,3,6,8-tetrachloro-2,7 naphthyridine (51 R = Cl) (Pd/C, H2, MeOH, AcOK 71 %)1374 cf 22 or indirect dechlorination of l-chloro-2,7-haphthyridine (51, R = H) by hydrazi-nolysis and subsequent oxidation (ILNNIL-ILO, EtOH, 100°C then CuS04, fUO 76% overall) 1279 also homologs.188... 

Dichlorprop and 2,4-D are structurally related dichlorinated phenoxy-acetic acid pesticides (see Table 1). The photochemistry of 2,4-D has been studied some time ago 2,4-dichlorophenol was found as the the main product [75]. More recent photoproduct analysis studies are available for dichlorprop [76,77]. Climent et al. identified several products corresponding to dechlorination on the one hand, and to decarboxylation on the other ho-molytic bond cleavage steps were proposed to take place [76]. In a later study, Meunier et al. were able to demonstrate that 4-chloropyrocatechol is the major primary photoproduct [77]. A heterolytic cleavage of the ether bond and of the C - Cl bond was put forward as a possible mechanism (Scheme 9). 

Chiral 4-hydroxy-2-cyclopentenones. Both (R)- and (S)-4-hydroxy-2-cyclo-pentenones can be obtained from phenol. The first step is alkaline hypochlorite oxidation to the acid 1, which is resolved with brucine. Oxidative decarboxylation of 1 gives 2, which is partially dechlorinated and protected as the silyl ether (3). The last step to 4 is reduction with zinc-silver (S, 760) or zinc-copper. ... 

One synthesis of cyclopentenone [80], requiring a resolution, involved initial ring contraction of phenol when treated with alkaline hypochlorite (49). Resolution of the resulting cis acid [85] was effected with brucine. The desired enantiomer [86] formed the more soluble brucine salt and was thus obtained from the mother liquors of the initial resolution. Oxidative decarboxylation with lead tetracetate, partial dechlorination with chro-mous chloride, and alcohol protection gave chloro enone [87]. Zinc-silver couple (50) dechlorinated [87] to the desired cyclopentenone [80]. 

The hrst rehable report of the preparation of tetrafluoroethene (TFE) was given in 1933 by Rulf and Bretschneider [643], who decomposed tetrafluoromethane in an electric arc. Other syntheses are based on the dechlorination of yn-chlorodifluoromethane [644], the pyrolysis of chlorodifluoromethane [645], and the decarboxylation of sodium perfluoroproprionate [646]. Since then, a number of synthetic routes have been developed [644-646]. On a laboratory scale, depolymerization of PTFE by heating at about 600 °C is probably the preferred method to obtain a smah amount of pure monomer (97%) [647], along with the highly toxic perfluoroisobutene as well as octafluorocyclobutane as a side product formed by the thermal (2ji -I- 2n) cyclodimerization of TFE [648,649]. The most common commercial approach for the preparation of TFE is the pyrolysis of chlorodifluoromethane [645,650]. The noncatalytic gas-phase reaction is carried out in a flow reactor at atmospheric pressure, yields over 95% TFE at 590 to 900 °C. The synthesis of TFE involves the following steps ... 

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