Chlorine occurence

In a process similar to that described in the previous item, the stored data can be used to identify not just a series of compounds but specific ones. For example, any compound containing a chlorine atom is obvious from its mass spectrum, since natural chlorine occurs as two isotopes, Cl and Cl, in a ratio of. 3 1. Thus its mass spectrum will have two molecular ions separated by two mass units (35 -i- 2 = 37) in an abundance ratio of 3 1. It becomes a trivial exercise for the computer to print out only those scans in which two ions are found separated by two mass units in the abundance ratio of 3 1 (Figure 36.10). This selection of only certain ion masses is called selected ion recording (SIR) or, sometimes, selected ion monitoring (SIM, an unfortunate... 

The kinetics of formation and hydrolysis of /-C H OCl have been investigated (262). The chemistry of alkyl hypochlorites, /-C H OCl in particular, has been extensively explored (247). /-Butyl hypochlorite reacts with a variety of olefins via a photoinduced radical chain process to give good yields of aUyflc chlorides (263). Steroid alcohols can be oxidized and chlorinated with /-C H OCl to give good yields of ketosteroids and chlorosteroids (264) (see Steroids). /-Butyl hypochlorite is a more satisfactory reagent than HOCl for /V-chlorination of amines (265). Sulfides are oxidized in excellent yields to sulfoxides without concomitant formation of sulfones (266). 2-Amino-1, 4-quinones are rapidly chlorinated at room temperature chlorination occurs specifically at the position adjacent to the amino group (267). Anhydropenicillin is converted almost quantitatively to its 6-methoxy derivative by /-C H OCl in methanol (268). Reaction of unsaturated hydroperoxides with /-C H OCl provides monocyclic and bicycHc chloroalkyl 1,2-dioxolanes. 

Chlorinated paraffins are manufactured by passing pure chlorine gas into a Hquid paraffin at a temperature between 80 and 100°C depending on the chain length of the paraffin feedstock. At these temperatures chlorination occurs exothermically and cooling is necessary to maintain the temperature at around 100°C. Catalysts are not usually necessary to initiate chlorination, but some manufacturers may assist the process with ultraviolet light. Failure to control... 

Replacement of hydrogen with halogen can be carried out in the alpha position of fluorinated ethers, amines, aldehydes, or nitriles In 2,2,3,4,4,4 hexafluoro-bulyl methyl ether, chlorination occurs predominantly at the methyl, however, bromination occurs mostly at the internal position of the fluorobutyl group 133] (equation 20)... 

Sodium chloride, by far the most abundant compound of chlorine, occurs in extensive evaporite deposits, saline lakes and brines, and in... 

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). 

Depending on the relative amounts of the two reactants and on the time allowed, a sequential substitution of the alkane hydrogen atoms by chlorine occurs, leading to a mixture of chlorinated products. Methane, for instance, reacts with CI2 to yield a mixture of CH3CI, CH2CI2, CHCI3, and CCI4. We ll look at this reaction in more detail in Section 5.3. 

Studies of chlorination and bromination of 2//-cyclopenta[reactivity differences dependent on substituents and halogenation conditions. In monochlorination the unsubstituted compound was more reactive than its 2-methyl and 2-phenyl derivatives, the reactivity ratio being 7.1 1.7 1 [78H(11)155]. Chlorination occurred most readily in the 5- and 7-positions of the cyclopentadienyl moiety, but once all three positions had been substituted, NCS attacked the methyl group... 

However, Schwarz s suggestion to focus on bonded atoms rather than neutral atoms also runs into a major problem because the atoms of any element typically show a large variety of oxidation states. For example, atoms of chlorine occur in the zero oxidation state in the chlorine molecule, the —1 state in NaCl, +1 in HOC1, +3 in HC102, +5 in HCIO3, and +7 in HCIO4. 

The evidence for this is based on the facts that (a) chlorine can be aspirated from the reaction mixture, (b) in the presence of more reactive aromatic compounds cross-chlorination occurs as in the reaction... 

Bromination of a-ergocriptine 2 with commercial N-bromosuccinimide (NBS) can lead to the formation of traces of a mysterious by-product, finally identified as 2-chloro-a-ergocryptine 4. Investigation of NBS indicated that it contains up to 1.5 % of chlorine (probably as N-chloro-succinimide, NCS). This chlorination occurs only in the presence of NBS, never with NCS alone ... 

An extension of the reduction-chlorination technique described so far, wherein reduction and chlorination occur simultaneously, is a process in which the oxide is first reduced and then chlorinated. This technique is particularly useful for chlorinating minerals which contain silica. The chlorination of silica (Si02) by chlorine, in the presence of carbon, occurs above about 1200 °C. However, the silica present in the silicate minerals readily undergoes chlorination at 800 °C. This reaction is undesirable because large amounts of chlorine are wasted to remove silica as silicon tetrachloride. Silica is, therefore, removed by other methods, as described below, before chlorination. Zircon, a typical silicate mineral, is heated with carbon in an electric furnace to form crude zirconium carbide or carbonitride. During this treatment, the silicon in the mineral escapes as the volatile oxide, silicon monoxide. This vapor, on contact with air, oxidizes to silica, which collects as a fine powder in the furnace off-gas handling system ... 

It is clear that when the formation of a higher chloride, by the interaction between a lower chloride and chlorine is difficult, the reverse reaction, i.e., the decomposition of the higher chloride to a lower chloride and chlorine, occurs easily. For example, vanadium tetrachloride decomposes, on heating at its boiling point (148.5 °C) to the trichloride and chlorine ... 

During hydrogenation of vinylic chlorides, both saturation of the double bond and hydrogenolysis of the C-Cl bond take place.433 35 Also, selective hydrogenolysis of chlorine occurs in the presence of fluorine atoms on a Pd/C catalyst (Scheme 4.125).436... 

The chlorination of hydrocarbons proceeds via the chain mechanism [195]. Chlorine atoms are generated photochemically or by the introduction of the initiator. However, liquid-phase chlorination occurs slowly in the dark in the absence of an initiator. The most probable reaction of thermal initiation in RH chlorination is the bimolecular reaction... 

As reviewed by Fereira et al. [104], the reaction of estrogens, that is estrone, estradiol, and ethinylestradiol, with free chlorine occurs mainly via an electrophilic substitution at the ortho and para positions, which results eventually in cleavage of the aromatic structure. Several authors have reported that dichlorinated derivatives present less estrogenic activity than monochlorinated derivatives, and in most cases, estrogen DBFs are less potent in terms of estrogenicity than the parent compounds. 

H-l,2,3-Benzodithiazol-6-ones 141 were prepared from p-benzoquinone-4-oximes, S2CI2, N-ethyldi/sopropylamine and NCS (1998T223 Scheme 72). Some ring chlorination occurred and 2,6-substituents were retained in the products except for the ferf-butyl group, which was replaced by chlorine. 1,4-Naphthoquinone 4-oxime and 1,2-naphthoquinone 2-oxime similarly gave dithiazole derivatives 142 and 143 (1998T223). 

With sulfur and triethylamine in dimethylformamide, compounds (86) give (89) (Equation (21)) <89JPR243>. With thiols or KjS, sulfides are produced (e.g., (90) and (91)), which show spasmolytic activity in vitro <86MI 404-01 >. Smooth 5N2-displacements of chlorine occur with phenol, thiophenol, SCN, and thiourea in dimethylsulfoxide. However, with K2CO3 or sodium cyanide, (86) (Ar = Ph) affords the trimers (92) or (93) (Scheme 32). With electron-deficient trans alkenes, stereoselective formation of cyclopropanes (94) was observed (Scheme 32). No reactions occur with maleates <66HCA412>. 

At low temperatures partial reduction of chlorine occurs, forming yellow unstable chloro derivatives, arsenic dihydrogen chloride and arsenic hydrogen dichloride ... 

Titanium reacts with all halogens at high temperatures. It reacts with fluorine at 150°C forming titanium tetrafluoride, TiF4. Reaction with chlorine occurs at 300°C giving tetrachloride TiCR. Bromine and iodine combine with the metal at 360°C forming their tetrahahdes. 

Certain elements, such as chlorine, occur in several very common isotopes, so their average atomic mass isn t close to a whole number. Other elements, such as carbon, occur in one very common isotope and several very rare ones, resulting in an average atomic mass that s very close to the whole-number mass of the most common isotope. 

Chlorine occurs in two common isotopes. It appears as j Cl 75.8% of the time and as jJCl 24.2% of the time. What is its average atomic mass ... 

Chlorine occurs mainly in seawater, in which chloride is the most abundant anion (19350 mg kg-1), and as rock salt (halite, NaCl) in evaporites. Elemental chlorine is important in sterilization of water supplies and production of chlorinated plastics such as polyvinyl chloride (PVC), but some chlorine compounds used extensively in the past, such as the insecticide... 

These substituted anthracenes react with CC1 in the same manner as anthracene. On heating the exposed solutions, new peaks appear at frequency differences Av = 780 30 cm-1 from the 0 —0 vibrational peak of the long wave band, due to photochlorination. Exception is found in the case of 9-methyl anthracene. No new peaks appear but only a wavelength shift of 2-3 nm is observed. Perhaps chlorination occurs in the —CHS group and the substitution of Cl-atom is not likely to change... 

Olah151 and later Messina152 found that PCI5 is a highly effective catalyst for the free-radical side-chain chlorination of arylalkanes. Chlorination in hydrocarbon or chlorinated solvents or without solvent at room temperature yields a monochlo-rinated products with high selectivity. When the reaction was carried out in polar solvents such as nitromethane and nitrobenzene, only ring chlorination occurred. 

In the production of carbon tetrachloride, chlorination is carried out in excess chlorine. The lower-boiling, partially chlorinated products then enter into a series of reactors where they react with added chlorine to achieve almost full chlorination of methane. In another process called chlorinolysis, higher aliphatic hydrocarbons undergo exhaustive chlorination at pyrolytic temperature (>600°C).177 182 183 Under such conditions carbon-carbon bond fission and simultaneous chlorination occur. Aliphatic hydrocarbon wastes are the preferred feedstock, as they react with about 20% excess chlorine. 

These results suggest that the replacement of the hydroxyl group at C-l by chlorine occurs by way of an intermediate chlorosulfate, resulting in an overall inversion of configuration moreover, they show that anomerization does not occur to any significant extent under the reaction conditions. 

Both thienothiophenes (3) and (7) were subjected to competitive electrophilic substitution reactions with thiophene. The fused heterocycles were always more reactive than thiophene in acetylation, Vilsmeier formylation and chlorination with NCS. While acetylation of both (3) and (7) occurrred at a comparable rate, formylation and chlorination occurred faster in the [3,2-6]-fused isomer (3) than in the [2,3-6] isomer (7). 

A very rare example of preferential photochemical reduction of an a-C-F bond rather than a //-chlorine occurs with chlorofluoropropanoates, in which this unusual selection in radical reactions is achieved by photochemical reduction.107 In oc.oc-difluoro esters 6 both C-F bonds can be reduced stepwise using hexamethylphosphoric triamide as the solvent and hydrogen donor.108 100... 

---