Question

Using Grignard reagent which of the following conversions takes place?
(A) The conversion of lower alcohol to higher alcohol
(B) The conversion of lower alkane to higher alkane
(C) Both A and B
(D) The conversion of the higher organic compound onto its lower homologues

Answer 1

Hint: The Grignard reagent is one of the most powerful tools of organometallic compounds in the field of organic chemistry and is used for the synthesis of alcohol.

Complete step by step solution:
-The chemical formula of the Grignard reagent of Grignard compound is R-Mg-X, where X is a halogen and R is an organic alkyl or aryl group.

-French chemist Victor Grignard in the year 1900 discovered Grignard reagent and 1912 was awarded the Nobel prize for the discovery.

-Methylmagnesium chloride$(Cl-Mg-C{{H}_{3}})$ and Phenylmagnesium bromide $({{C}_{6}}{{H}_{5}}-Mg-Br)$ are the two examples and subclasses of organomagnesium compounds.

-Pure Grignard reagents are extremely reactive solids, hence are normally handled as solutions in solvents such as diethyl ether and tetrahydrofuran which are relatively stable as long as the water is excluded. Grignard reagent in such mediums is invariably present as a complex with the magnesium atom connected to the other two oxygen by coordination bonds.

-Grignard reagent exhibits strong nucleophilic qualities and also have the ability to form new carbon-carbon bonds.

-The mechanism for the preparation of Grignard reagent is as follows-

\[\begin{align}
 & R-X+Mg\to R-{{X}^{\centerdot -}}+M{{g}^{\centerdot }}^{+} \\
 & R-{{X}^{\centerdot -}}\to {{R}^{\centerdot }}+{{X}^{-}} \\
 & {{R}^{\centerdot }}+M{{g}^{\centerdot +}}\to RM{{g}^{+}} \\
 & RM{{g}^{+}}+{{X}^{-}}\to RMgX \\
\end{align}\]

-By Wurtz reaction, the carbon chain of a compound can be increased from lower alcohol to higher alcohol using Grignard’s reagent.

$C{{H}_{3}}C{{H}_{2}}OH\xrightarrow{HBr}C{{H}_{3}}C{{H}_{2}}Br\xrightarrow[+BrC{{H}_{2}}C{{H}_{3}}]{+2Na}C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}C{{H}_{3}}\xrightarrow{B{{r}_{2}},h\upsilon }C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}C{{H}_{2}}Br\xrightarrow{aq.KOH}C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}C{{H}_{2}}OH$

So, the correct answer is option A.

Note: The most common application of the Grignard reagent is the alkylation of aldehyde and ketone which usually involves an aqueous acidic workup. The Felkin-Anh model or Cram’s rule can be used to predict which type of stereoisomer will be formed while adding a Grignard reagent to an aldehyde or a prochiral ketone. Grignard reagents are strong nucleophiles for aliphatic substitutions with alkyl halides. Grignard reagents also serve as a base or protic substrates and react with alcohols, phenols, etc giving alkoxide (ROMgBr). Grignard reagents like organolithium compounds are also useful for forming carbon-heteroatom bonds.