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The carbonylation of methanol with carbon monoxide to methyl formate (methyl methanoate) is catalyzed by strong bases, such as potassium methoxide. [ 7 ] [ 8 ] The main application of potassium methoxide is use as basic transesterification catalyst in biodiesel synthesis (as a 25-32% methanolic solution).
tert-Butoxide, on the other hand, is a strong base, but a poor nucleophile, because of its three methyl groups hindering its approach to the carbon. Nucleophile strength is also affected by charge and electronegativity : nucleophilicity increases with increasing negative charge and decreasing electronegativity.
A hydroxide ion acting as a nucleophile in an S N 2 reaction, converting a haloalkane into an alcohol. In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they ...
The nucleophile may be electrically neutral or negatively charged, whereas the substrate is typically neutral or positively charged. An example of nucleophilic substitution is the hydrolysis of an alkyl bromide , R-Br under basic conditions, where the attacking nucleophile is hydroxyl ( OH − ) and the leaving group is bromide ( Br − ).
The following year a similar mechanism was proposed where oxidative addition of an aryl halide followed by migratory CO insertion and is followed by nucleophilic abstraction of the α-acyl by MeOH. One of the advantages of this intermolecular nucleophilic abstraction is the production of linear acyl derivatives.
Protic solvents react with strong nucleophiles with good basic character in an acid/base fashion, thus decreasing or removing the nucleophilic nature of the nucleophile. The following table shows the effect of solvent polarity on the relative reaction rates of the S N 2 reaction of 1-bromobutane with azide (N 3 – ).
Here, a strong Lewis acid is required to generate either a carbocation from an alkyl halide in the Friedel-Crafts alkylation reaction or an acylium ion from an acyl halide. In the vast majority of cases, reactions that involve leaving group activation generate a cation in a separate step, before either nucleophilic attack or elimination.
For example, protonation of methanol gives an electrophilic methylating reagent that reacts by the S N 2 pathway: CH 3 OH + H + → [CH 3 OH 2] + Similarly, methyl iodide and methyl triflate are viewed as the equivalent of the methyl cation because they readily undergo S N 2 reactions by weak nucleophiles. The methyl cation has been detected in ...