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Formation of Dichlorocarbene

Dichlorocarbene (Cl C) can be made from chloroform (CHCy, and a strong base such as tert-butoxide, (CH l CO or potassium hydroxide. Chloroform has three electron ative chlorine atoms, which inductively withdraw electron density from the carbon atom. Thus, the hydrogen atom of CHCI3 is much more acidic than the hydrogen atom of an alkane. The hase removes a proton from CHCI3, leaving the electron pair with the carbon atom. The product is a carhanion, the trichloro-methanide ion. [Pg.208]

The trichloromethanide ion loses a chloride ion to form dichlorocarbene, which is electrically neutral. Note that the electrons of the C —Cl bond leave with the chloride ion. [Pg.209]

The sum of the two steps corresponds to an ehmination reaction. The loss of two atoms or groups of atoms from the same carbon atom is called an a ehmination reaction. [Pg.209]


The idea that dichlorocarbene is an intermediate in the basic hydrolysis of chloroform is now one hundred years old. It was first suggested by Geuther in 1862 to explain the formation of carbon monoxide, in addition to formate ions, in the reaction of chloroform (and similarly, bromoform) with alkali. At the end of the last century Nef interpreted several well-known reactions involving chloroform and a base in terms of the intermediate formation of dichlorocarbene. These reactions included the ring expansion of pyrroles to pyridines and of indoles to quinolines, as well as the Hofmann carbylamine test for primary amines and the Reimer-Tiemann formylation of phenols. [Pg.58]

During the next fifty years the interest in derivatives of divalent carbon was mainly confined to methylene (CHg) and substituted methylenes obtained by decomposition of the corresponding diazo compounds this phase has been fully reviewed by Huisgen. The first convincing evidence for the formation of dichlorocarbene from chloroform was presented by Hine in 1950. Kinetic studies of the basic hydrolysis of chloroform in aqueous dioxane led to the suggestion that the rate-determining step was loss of chloride ion from the tri-chloromethyl anion which is formed in a rapid pre-equilibrium with hydroxide ions ... [Pg.58]

The actual formylation process is preceded by the formation of dichlorocarbene 3 as the reactive species. In strongly alkaline solution, the chloroform is deproto-nated the resulting trichloromethide anion decomposes into dichlorocarbene and a chloride anion ... [Pg.238]

Mechanism of the formation of dichlorocarbene by reaction of chloroform with strong base,... [Pg.227]

The most common example is formation of dichlorocarbene by treatment of chloroform with a base (see Reaction 10-3) and geminal alkyl dihalides with Me3Sn but many other examples are known, such as... [Pg.250]

At this point a benzaldehyde dimethylaeetal is used for the acetah-/ation. The thermodynamically favored six-membered acetal 15 is formed preferentially over the potential competitors five- and sev-cn-membereil acetals5 (See Chapter 7). Transformation of a primary alcohol function into the triflate group of structure 16 must precede the Sn2 reaction in the third step, in which a carbon nucleophile is created with LDA and chloroform. Dcprolonalion of chloroform with LDA is carried out at -110 C to suppress competing formation of dichlorocarbene.6... [Pg.221]

Formation of dichlorocarbene ( CC12) is also thought to occur by the simultaneous formation of two chlorine atoms ... [Pg.462]

Some a-eliminations have already been discussed, like the formation of dichlorocarbene from chloroform and base. Others will be presented in certain contexts later. 1,3-Eliminations are mentioned in the preparation of 1,3-dipoles such as diazoalkanes or a-diazoketones and nitrile oxides (Chapter 15). Chapter 4 is limited to a discussion of the most important eliminations, which are the alkene-forming, /3-eliminations. Note that /3-Eliminations in which at least one of the leaving groups is removed from a heteroatom are considered to he oxidations. Eliminations of this type are therefore not treated here hut in the redox chapter (mainly in Section 17.3.1). [Pg.158]

Phenols react with chloroform in the presence of hydroxide ion in water to give o- and jp-hydroxybenzaldehydes. The steps of the reaction are (1) the formation of dichlorocarbene, as shown in Example 4.22 (2) nucleophilic reaction of the phenoxide with the electrophilic carbene and (3) hydrolysis. [Pg.229]

Direct spectroscopic evidence for the formation of dichlorocarbene by irradiation of dichloroketene in an argon matrix... [Pg.439]

Of the many methods used for dichlorocyclopropanation of alkenes, the formation of dichlorocarbene from chloroform and base/phase-transfer catalyst and its subsequent reaction with an alkene is strongly recommended. In fact, since inception this method has been the most frequently used for the preparation of 1,1-dichlorocyclopropanes. ... [Pg.623]

According to the matrix IR spectra, the preferred formation of dichlorocarbene along with SiCU (1 3 60(1-620 cm ) or GeCl4 (1 3 445-465 cm ) has been also observed under vacuum pyrolysis (500-1000°C, lO -lO Torr) of trichloromethyltrichlorosilane and trichloromethyltrichlorogermane (Scheme 3). The CCI3 radical was formed in substantially lower amounts (Svyatkin et al., 1977 Nefedov et al., 1976). [Pg.10]

Furthermore, /8-cyclodextrin shows superb selectivity in the syntheses of 2.5-cyclohexadienones (12), which are important starting materials for the syntheses of physiologically active compounds, from / -substituted phenols, chloroform, and sodium hydroxide (Scheme 7) [25]. The selectivity of the production of 12 in the presence of /8-cyclodextrin is virtually 100%, in contrast to the formation of large amounts (about 4-8 times as large as 12) of ori/jo-formulated compound 13 in its absence. The remarkable selectivity in the present reaction is probably due to the formation of dichlorocarbene from chloroform and hydroxide ion in the cavity of /8-cyclodextrin. The / ara-substituted phenol should approach the cavity (and thus the carbene) from the side involving the para-ca.rhon, resulting in a selective reaction. The penetration of this apolar side in the apolar cavity should be more favorable than the penetration of the polar side by the phenoxide atom. [Pg.518]

The alkali-metal salts of PDM are very stable in ether containing DMSO or 18-crown-6 ether. However, in the absence of such components, they decompose at room temperature. At low temperatures, the major product is l//,2//-icosachlorotetraphenylethane, but at 36°C it becomes the a/f,a/f-decachlorodiphenylmethane (Ballester et al., 1968, 1973 Ballester and Olivella, 1974 Barrios, 1989). To account for the resulting products, a carbene mechanism has been suggested (135), as in the well-known formation of dichlorocarbene from CI3C M". ... [Pg.360]

Formation of Dichlorocarbene and Its Reaction with Cyclohexene (Section 15.sb)... [Pg.22]

Mechanism of the formation of dichlorocarbene by reaction of chloroform with strong base. Deprotonation of CHCI3 gives the trichloromethanide anion, " CCl3, which spontaneously expels a Cl ion. [Pg.287]

Both phase transfer and crown ether catalysts have been used to promote a eliminations from chloroform and other haloalkanes. " Various trialkylammonium hydroxides catalyze formation of dichlorocarbene in the organic phase of two phase systems consisting of CHCI3 and 50% sodium hydroxide solution. [Pg.433]


See other pages where Formation of Dichlorocarbene is mentioned: [Pg.69]    [Pg.237]    [Pg.304]    [Pg.70]    [Pg.128]    [Pg.1013]    [Pg.1278]    [Pg.805]    [Pg.621]    [Pg.9]    [Pg.621]    [Pg.805]    [Pg.621]    [Pg.1013]    [Pg.1280]    [Pg.258]    [Pg.208]   


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