What forms when an alkene reacts with OsO4?
Oxidation of alkenes Alkenes add to OsO4 to give diolate species that hydrolyze to cis-diols. The net process is called dihydroxylation. This proceeds via a [3 + 2] cycloaddition reaction between the OsO4 and alkene to form an intermediate osmate ester which rapidly hydrolyses to yield the vicinal diol.
What is a dihydroxylation reaction?
Dihydroxylation is the process by which an alkene is converted into a vicinal diol. Although there are many routes to accomplish this oxidation, the most common and direct processes use a high-oxidation-state transition metal (typically osmium or manganese).
What are the two possible stereochemical outcomes for dihydroxylation?
Alkenes can be dihydroxylated by two different stereochemical pathways: anti-dihydroxylation or syn-dihydroxylation. The opening of epoxides follows the anti-dihydroxylation mechanism, while potassium permanganate or osmium tetroxide produce the syn-dihydroxylated products.
Why KMnO4 is preferred over OsO4 for hydroxylation of alkene?
Since it is a strong oxidizing agent, it may cleave the C-C bond of the diol and oxidize it further to a carbonyl. In acid and neutral solution, it always does so; hence a basic solution of the permanganate must be used at low temperatures. OsO4, on the other hand, is more selective for preparing cis-diols.
What does oso4 do as a reagent?
Osmium tetroxide (OsO4) is a volatile liquid that is most useful for the synthesis of 1,2 diols from alkenes. (Side note: another name for 1,2 diols is vicinal diols, or vic-diols). The reaction is very mild, and usefully leads to the formation of syn diols. Another side note: this reaction doesn’t work with alkynes.
How does oso4 react?
Osmium tetroxide reacts with double bonds to form cyclic osmate(VI) diesters (10), which can then be hydrolyzed to provide vicinal diols in good yields. If, however, sodium periodate is also present, the diol is cleaved, as in Scheme 2, and carbonyl compounds are the final products.
What happens when an alkene reacts with osmium tetroxide?
When an alkene reacts with osmium tetroxide, stereocenters can form in the glycol product. Cis alkenes give meso products and trans alkenes give racemic mixtures.
What happens in the electrophilic addition of alkenes?
Electrophilic addition happens in many of the reactions of compounds containing carbon-carbon double bonds – the alkenes. Reactions of Alkenes with Hydrogen Halides This page gives you the facts and a simple, uncluttered mechanism for the electrophilic addition reactions between the hydrogen halides and alkenes li…
How does syn dihydroxylation of olefins take place?
Syn -dihydroxylation of olefins occur via the reaction with osmium tetroxide. Cycloaddition of osmium tetroxide with ethene proceeds via a cyclic transition state to form an osmate ester. Addition occurs on the same side of the ethene molecule to give a syn -addition. Work-up with water gives the syn -diol and reduced Osmium (VI).
What happens when an alkene reacts with sulfuric acid?
Alkenes react with concentrated sulfuric acid in the cold to produce alkyl hydrogensulphates. For example, ethene reacts to give ethyl hydrogensulphate. The structure of the product molecule is sometimes written as C H 3 C H 2 H S O 4, b ut the version in the equation is better because it shows how all the atoms are linked up.