Halogenation activity

Aryl halides with a halogen activated by electron-withdrawing groups react with pyrrolidine enamines of cyclic ketones (68) to give the a-arylated ketones after hydrolysis. The enamine (28) with 2,4-dinitrochlorobenzene gave an excellent yield of 2(2,4-dinitrophenyl)cyclohexanone (88). The... 

Dehydration-Halogenation-Activation and Silylation of Inorganic and Organic Salts and Metallorganic Compounds... 

I 73 Dehydration-Halogenation-Activation and Silylation of Inorganic and Organic Salts Bu NF ------------------------------------------ +Me3SiF7lf... 

Laturnus F, Adams FC, Gomez I, Mehrtens G (1997) Halogenating activities detected in Antarctic macroalgae. Polar Biol 17 281-284... 

The present procedure is applicable only to bromomalononitrile various a-halogen active methylene derivatives, (e.g., diethyl chloromalonate, methyl bromoacetoacetate) led predominantly to the formation of ring-contracted styrene derivatives. On the other hand, substituted cycloheptatrienylium salts with bromomalononitrile gave the desired dicyanoheptafulvene derivatives in excellent yields. One notable example is the synthesis of 5- and 7-(dicyanomethylene)-2,3-dihydrocyclohepta-1,4-dithiins.6... 

Chemical attack on membrane U-1 is revealed by increasing product flux which is evidently related to breaking chemical bonds within the polymer. Membranes A-2 and X-2 respond to chemical attack by decreased product flux which probably results from halogen addition to these polymers. On this basis, the order of halogen activity below pH 5.8 is Br2 > Cl2 > l2- With membrane U-1 at pH 8.6 the order changes to Cl2 > Br2 > l2- One may conclude that... 

The protons of pyrimidines, pyrazines and pyridazines are relatively acidic even without halogen activation, and the three simple heterocycles 240-242 have been lithiated (with varying success) with LiTMP (Scheme 120). ... 

Sander, R., and P. Crutzen, Model Study Indicating Halogen Activation and Ozone Destruction in Polluted Air Masses Transported to the Sea, J. Geophys. Res., 101, 9121-9138 (1996). 

It should be explored whether halogen activation reactions may also occur under different circumstances than at polar sunrise (33, 34). Recent observational studies by Ayers and colleagues at Cape Grim, Tasmania, indicate Br release from seasalt (35). 

Sander, R and P.J, Crntzen (1996) Model study indicating halogen activation and ozone destruction in polluted air masses transported to the sea, J. Geophys. Res., 101,9121-9138. 

Tables on the "reaction probalility or "uptake coefficient" have been summarized for various heterogeneous reactions in a recent review article [87], and by the IUPAC [88] and NASA-JPL [86] evaluation teams. For the purpose of this article, a rough comparison is made of the uptake rates for the reactions (1) to (5) on the different type surfaces. Three major type of surfaces have been considered a) NAT, or Type I PSC, b) Water ice, or Type II PSC and c) sulfuric acid aerosol, which is normally a liquid surface generally composed of 60-80 wt % H,S04 and 40-20 wt % H,0 also considered is the solid form SAT (sulfuric acid tetrahydrate) with a composition of 57.5 wt % H,S04. The importance of chlorine activation on sulfuric acid solutions has been demonstrated in a recent article [89]. Halogen activation on seasalt material will shortly be reviewed as part of the tropospheric processes.

Hasan Z, Renirie R, KerkmanR, Ruijssenaars HJ, Hartog AF, Wever R (2006) Laboratory-Evolved Vanadium Chloroperoxidase Exhibits 100-Fold Higher Halogenating Activity at Alkaline pH. Catalytic Effects from First and Second Coordination Sphere Mutations. J Biol Chem 281 9738... 

Mehrtens G, Latumus F (1997) Halogenating Activity in an Arctic Population of Brown Macroalga Laminaria saccharina (L.) Lamour. Polar Res 16 19... 

Hasan, Z., Renirie, R., Kerkman, R., Ruijssenaars, H.J., Hartog, A.F. and Wever, R. (2006) Laboratory-evolved vanadium chloroperoxidase Exhibits 100-fold higher halogenating activity at alkaline pH catalytic effects from first and second coordination sphere mutations. 

According to a report by Goldberg and Alper55, protonation of NXS (X = Cl or Br) with a strong, highly lipophilic acid such as perchloric acid can generate positive halonium species capable of halogenating activated aromatics (e.g. mesitylene) and heteroaromatics (e.g. thiophene) in a catalytic manner in low-polarity media. They provided the scheme shown in equation 38. Since this is a biphasic system, perchloric acid should act as phase-... 

There are several examples of haloperoxidases containing metals other than iron, and many of these are non-heme enzymes. For example, a series of bromoperoxidases have been isolated recently from seaweed17,18 and an actinomycete19 that require vanadium for halogenating activity. 

Double and Triple 11.4 Addition of Halogens Active figures... 

Direct, two-electron oxidations are rare for most peroxidase enzymes. The one broad exception is the oxidation of halide and pseudohalide ions, specifically F, Br , Cl-, and NCS . Fluoride ion, in contrast, is not known to be oxidized by these enzymes. The oxidation of F and NCS" is common for the peroxidases, whereas that of Br is widespread but is usually less effective, and that of Cl , among the conventional peroxidases, is only important in the case of MPO [46, 83]. The halogenation activities of the mammalian peroxidases are compared in Table 5.3. As the table shows, chloride ion is oxidized by MPO, particularly at pH 5, but it is a very poor substrate for EPO and LPO. Br , F, and SCN" are readily oxidized by all three enzymes, but most efficiently by EPO at pH 5 [84—86]. 

Table 9 Experimental Tafel Slopes, Charge Transfer Coefficients and Surface Coverages for Halogen-Active Carbon Electrodes at Various Temperatures and Coverages... 

Try the following problems to practise using the metal and halogen activity series to predict whether reactions will occur. 

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