Isomers 1.2- dichloroethane

Cresol/cresylic acid (mixed isomers) dichloroethane)... 

Trichloroethane is also a coproduct in the thermal and photochemical chlorination of 1,1-dichloroethane to produce 1,1,1-trichloroethane. Vapor chlorination favors the 1,1,1-isomer, whereas reaction in the Hquid phase may give much higher ratios of 1,1,2-trichloroethane. V-type 2eohtes have been used in vapor-phase chlorination of 1,1-dichloroethane to produce 1,1,2-trichloroethane in high selectivity (100). 

SUMICHIRAL OA-25001 is available from Sumitomo Chemical Co., Ltd. The eluent was hexane/1,2-dichloroethane/ethanol, 200 40 1, with a flow rate of 0.5 mL/min, and detection by 254 nm light. The tR of the (R)-isomer (16.8 min) is shorter than that of the (S)-isomer (18.3 min). The checkers used a CHIRACEL OC column supplied by Daicel Chemical Industries, Ltd., with 10% isopropyl alcohol/heptane as the mobile phase. 

Cyclopentadiene forms a mixture of the 1,2- and 1,4-adducts in equal proportions. However, the 1,2-isomer rearranged completely into the thermodynamically more stable 1,4-isomer after prolonged standing in the solvent (alcohol or dichloroethane). 

The concept of atropisomerism developed to a considerable extent following other developments in chemistry, especially those in spectroscopy. Early work by Kohlrausch (4) and Mizushima (3), based on Raman spectra and dipole moment studies, established that rotational isomers—rotamers—must exist in 1,2-dichloroethane. Pitzer established that there are three energy minima when ethane is rotated about its C—C axis (6). Rotamers about single bonds have been found in a wide variety of organic compounds since then, mainly as a result of the application of vibrational spectroscopy to organic molecules (7). 

In principle, separation of resonances of diastereomeric compounds (such as dl and meso isomers) may be increased simply through use of an appropriate achiral solvent. Chiral solvents may in some cases be especially effective in producing a separation, particularly if the diastereomers differ in configuration about a center that is amenable to analysis by the CSA method. Kaehler and Rehse (89) give a detailed account of conditions necessary for measurement of the ratio of meso- and dZ-tartaric acid employing A,N-dimethyl PEA. Bomyl acetate used as solvent for l,2-difluoro-l,2-dichloroethane (90) allows measurement of the diastereomeric composition. Paquette and co-workers (91,92), using TFAE, were able to determine the diastereomeric purity of the recrystallized adducts 47 of... 

More ways are not possible because of limitations on the number of bonds each type of atom can carry (carbon has a limit of four, hydrogen and chlorine have a limit of one each). But the important lesson here is that the two molecules shown (1,1-dichloroethane and 1,2-dichloroethane) are different chemicals. They have identical numbers of C, H, and Cl atoms ( isomer means same weight ) but different chemical structures. 

The formation of -isomers during acylation of the unsubstituted thienothiophenes 1 and 2 was reported first in 1972 by Bugge, who showed by gas-liquid chromatography and mass spectrometry that thienothiophenes 1 and 2 with acetic anhydride and SnCl4 in dichloroethane at 25° affords the 2-acetyl derivatives (80% yields), containing up to 1% of 3-acetylthieno[2,3-6]thiophene and 0.8% of 3-acetylthieno[3,2-h]thiophene. 

The other possible isomer, 1,4-dimethylpyrazole (and its other N-alkyl and -aryl analogues), reacted with chlorine in dichloroethane at 25-35°C to produce 5-chloro derivatives in around 70% yields (90EUP366329). 5-Aryl-3-methylpyrazoles were chlorinated by NCS at C-4 (86JHC459), as were a range of pyrazoles by chloroperoxidase in the presence of hydrogen peroxide and potassium chloride at pH 2.9. Yields of 68-83% make this latter process an improvement over some traditional chemical methods (87JHC1313). 

DICHLOROETHANE AND DERIVATIVES Dichloroethane, Ethylene Dichloride or Ethylidene Dichloride, C2H4CI2 mw 98.97. Two isomers are possible ... 

Most of the side reactions have already been discussed in Section 26.1.3.3. (dediazoniation in organic solvents). Chlorinated aliphatic solvents, such as 1,2-dichloroethane and dichloro-methane, lead to an extensive formation of chloroaromatics, and aromatic solvents, even halogenated examples, can be arylated to some extent by arenediazonium tetrafluoroborates (vide supra). For example, during dediazoniation of benzenediazonium tetrafluoroborate in toluene, chlorobenzene, bromobenzene or anisole, 3-5 % of substituted biphenyls Ph-C6H4-X (X = Me, Cl, Br, OMe) are formed together with 0.5-0.8% of fluorobiphenyls.5 Fluorobiphenyls are formed through an ionic pathway (only 2- and 4-isomers are formed) whereas chlorobiphenyls result from a radical process (X = Cl, 2-/3-/4-isomer 26 47 27).243... 

As a result, free-radical chlorination of alkanes is a nonselective process. Except when only one type of replaceable hydrogen is present (methane, ethane, neopentane, unsubstituted cycloalkanes), all possible monochlorinated isomers are usually formed. Although alkyl chlorides are somewhat less reactive than alkanes, di- and polychlorinations always occur. The presence of a chlorine atom on a carbon atom tends to hinder further substitution at that carbon. The one exception is ethane that yields more 1,1-dichloroethane than 1,2-dichloroethane. The reason for this is that chlorination of an alkyl chloride occurs extremely slowly on the carbon atom adjacent to the one bearing the chlorine atom (vicinal effect).115... 

Fig. 15 Separation of the phenacyl derivatives of the geometrical isomers of (A) linoleic and (B) linolenic acids by HPLC in the silver ion mode. The column temperature was 38°C, and the mobile phase was 1,2-dichloroethane/dichloromethane/acetonitrile (49.75 49.75 0.5 v/v/v) at a flow rate of 0.75 ml/min, with detection at 242 nm. Note the change of scale on the time axis.

Laali et al.234 have developed a method to the highly selective pura-adamantylation of arenes (toluene, ethylbenzene, anisole) with haloadamantanes (1-chloro- and 1-bromoadamantane, l-bromo-3,5,7-trimethyladamantane) and 1-adamantanol promoted by triflic acid in butylmethylimidazolium triflate [BMIM][OTf] ionic liquid. In contrast to reactions mn in 1,2-dichloroethane, little or no adamantane byproduct was detected in [BMIM][OTf. Furthermore, no isomerization of para-tolyladamantane was observed supporting the intramolecular nature of the formation of meta isomers. In competitive experiments with benzene-toluene mixture (1 1 molar ratio), high substrate selectivities were found (kT/kB = 16-17) irrespective of the alkylating agent. This is in sharp contrast to values about unity measured in 1,2-dichloroethane. 

Reaction of 2-aminopyridines and A/,/V-disubstituted malonamates afforded mixtures of 4-amino-2-oxo-2f/- and 2-amino-4-oxo-4//-pyrido[ 1,2-nlpyrimidines 78 and 79 in boiling 1,2-dichloroethane with phosphoryl chloride (82FES747 87JHC329 88FES705). Generally the ratio of the 2-oxo and 4-oxo isomers 78 and 79 increased in the presence of bulkier R and/or R1 groups (see Table VIII). 

Yoshino (51) studied the abundance ratios of the gauche and trans forms of dichloroethane and the keto-enol isomers of acetyl acetone when these compounds were adsorbed (less than monolayer quantities) on silica gel. The gauche-trans ratio, which is unity in chloroform solution and 1.4 in the pure liquid, was found to be 1.9 in the adsorbed state. The 1430-cm.-1 gauche band and the 1450-cm.-1 trans band were not affected by the adsorption. The absorption bands of acetyl acetone were measured for a 1.5 % chloroform solution, the pure liquid, liquid saturated with water, and the adsorbed state. The relative intensity of the 1600-cin. 1 enol band and the 700-cm.-1 keto baud were used to determine the isomer ratio. The 1600-... 

Fish and co-workers have studied N-to-77 rearrangements of a number of cyclopentadienyl rhodium and ruthenium complexes of pyridines and quinolines. This behavior was first observed in the complex [Ru(C5H5)(CH3CN)2(2-Mepy)]+ where the cr-bound N-isomer (15) gave an equilibrium mixture of the N- and w-bound (16) complexes on heating in 1,2-dichloroethane (ratio 15 16 = 6 1). No free ligand was detected in... 

It should be noted that mixtures of isomers are involved in many cases of organic solvents e.g., mixed xylene isomers, mixed cis- and trans-decalin, mixed 1,1- and 1,2-dichloroethane, or mixed cresols, without obvious detrimental effects on the particular application attempted. However, in the following it is assumed that definite single substances are to be dealt with. 

A drawback of the resulting intrinsic volume is that it does not distinguish between isomers, not only geometrical ones, such as 1,1-dichloro- and 1,2- dichloroethane, both having Vx = 63.5 cm3 mol 1, but also structural ones, such as 1-butanol and diethyl ether, both having Vx = 73.1 cm3 mol1. The Vx values, shown in Table 3. 4, are nearly proportional to the van der Waals intrinsic... 

The reaction temperature had a dramatic impact on the enantioselectivity of the silane addition. Using acetophenone, diphenylsilane and the (S-Binap)Rh(PPh3)2 catalyst as a model system, the initial reaction temperature was varied from -40°C to 55°C. When carried out under the standard conditions (vide supra), the reduction gave an optical yield of 26% (5-isomer). Lowering the initial temperature to 0°C caused a decrease in the e.e. to 12% and decreasing the temperature further still to -40°C resulted in an optical yield of only 7%. Increasing the initial temperature, on the other hand, to 55°C (1,2-dichloroethane solvent) raised the optical yield to 55%. 

Dichloro-bis (2,4-pentanedionato) zirconium(IV) is monomeric and a weak electrolyte in nitrobenzene solution n.m.r. chemical shifts,7 infrared and Raman spectra,8 and dipole-moment studies21 indicate that this compound exists in solution as the octahedral cis geometrical isomer. Chloro- and bromotris(2,4-pentanedionato) zirconium (IV) are seven-coordinate complexes which are monomeric in benzene and only slightly dissociated in nitrobenzene and 1,2-dichloroethane. Iodotris(2,4-pen-tanedionato) zirconium (IV), however, is appreciably dissociated both in nitrobenzene and in 1,2-dichloroethane.7... 

Finally, I identified another factor, a variable air leak. When I eliminated this, both dichloroethanes decomposed slowly by the unimolecular mechanism. When I let in a controlled flow of air (or chlorine), the 1,2-dichloroethane (in contrast to the 1,1-isomer) now decomposed rapidly at a much lower temperature. I had discovered my first new reaction the radical chain decomposition of the dichloride as in Scheme 2. 

Direct oxidation of the lesser chlorinated ethenes, ethanes, polychlorinated benzenes, and chlorobenzene has been reported. Wiedemeier et al. [25] summarize a number of studies that report direct aerobic oxidation of vinyl chloride (VC), 1,2-dichloroethane, the three dichlorobenzene isomers, 1,2,4-trichlorobenzene, and 1,2,4,5-tetrachlorobenzene. Bradley [33] reports that DCE has served as a primary substrate for energy production with oxygen as the electron acceptor, though use of DCE as a sole carbon source has not been demonstrated. Rittmann and McCarty [29] also report that the two least chlorinated methanes (dichloromethane and chloromethane) as well as chloroethane can be directly oxidized under aerobic conditions. Direct oxidation of the chlorinated compounds is typically modeled using either first-order or Monod kinetics [29,31]. 

In the older organic chemistry it was assumed that a free rotation was possible about a single C—C bond because, for example, there exist no isolatable isomers of 1,2 dichloroethane. Accurate measurements of the specific heat of ethane at low temperatures and likewise the difference between determinations and calculations of equilibria of hydrocarbons have, however, shown that there is no question of a free rotation rotation is indeed possible but there is a potential barrier of about 3 kcal/mole which has to be surmounted. The state of lowest energy is that in which the two methyl groups, or the methyl and the CH2 group, are alternate. In 1, 2 dichloroethane etc. there appear to be two positions of (relatively) minimum energy, the trans position and an oblique position which lies 1.2 kcal higher than the former. 

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