Preparation Questions in English

(D) Collin's reagent is a complex of chromium trioxide with pyridine,represented by the formula $CrO_3 \cdot 2C_5H_5N$.
It is used for the selective oxidation of primary alcohols to aldehydes and secondary alcohols to ketones without over-oxidation to carboxylic acids.

(B) The oxidation of benzyl chloride $(C_6H_5CH_2Cl)$ with lead nitrate $(Pb(NO_3)_2)$ is a specific reaction used to prepare benzaldehyde $(C_6H_5CHO)$.
This reaction involves the conversion of the $-CH_2Cl$ group into a $-CHO$ group.
The reaction can be represented as:
$C_6H_5CH_2Cl \xrightarrow{Pb(NO_3)_2} C_6H_5CHO$
Therefore,the correct option is $(b)$.

(D) The reduction of an acid chloride with $H_2$ in the presence of $Pd$ supported on $BaSO_4$ (poisoned with sulfur or quinoline) is known as the Rosenmund reduction.
This reaction specifically reduces the acid chloride to an aldehyde.
For acetyl chloride $(CH_3COCl)$:
$CH_3COCl + H_2 \xrightarrow{Pd/BaSO_4} CH_3CHO + HCl$
Thus,the product is acetaldehyde $(CH_3CHO)$.

(B) . When glycerol is heated with a dehydrating agent like concentrated $H_2SO_4$ or $KHSO_4$,it undergoes dehydration to form acrolein (propenal),which has a characteristic pungent (bad) odour.
$CH_2OH-CHOH-CH_2OH \xrightarrow{\text{conc. } H_2SO_4, \Delta} CH_2=CH-CHO + 2H_2O$

(B) The catalytic oxidation of methanol $(CH_3OH)$ in the presence of silver $(Ag)$ catalyst at $600\,^oC$ leads to the formation of formaldehyde ($H_2C=O$ or $HCHO$).
The reaction is: $2CH_3OH + O_2 \xrightarrow{Ag, 600\,^oC} 2HCHO + 2H_2O$.

(B) The oxidation of a primary alcohol $(CH_3CH_2OH)$ proceeds in two steps:
$1$. First,the primary alcohol is oxidized to an aldehyde $(CH_3CHO)$.
$2$. Then,the aldehyde is further oxidized to a carboxylic acid $(CH_3COOH)$.
In the given reaction sequence,$CH_3CH_2OH$ $\xrightarrow{[O]}$ $X$ $\xrightarrow{[O]}$ $CH_3COOH$,$X$ represents the intermediate product,which is acetaldehyde $(CH_3CHO)$.

(A) The given compound $CH_3-CH(OH)-CN$ is formed by the nucleophilic addition of hydrogen cyanide $(HCN)$ to acetaldehyde $(CH_3CHO)$.
This reaction is a characteristic reaction of aldehydes and ketones.
The product formed is known as a cyanohydrin.
Specifically,since it is derived from acetaldehyde,it is called acetaldehyde cyanohydrin.

(C) The reaction of an acid chloride with $H_2$ in the presence of $Pd-BaSO_4$ is known as the Rosenmund reduction.
This reaction specifically reduces the acid chloride group $(-COCl)$ to an aldehyde group $(-CHO)$.
Therefore,the product $P$ is $RCHO$.

(D) Acetophenone can be prepared by Friedel-Crafts acylation.
Benzene reacts with acetyl chloride in the presence of anhydrous aluminum chloride $(AlCl_3)$ to form acetophenone $(C_6H_5COCH_3)$ and hydrogen chloride $(HCl)$.
The reaction is:
$C_6H_6 + CH_3COCl \xrightarrow{Anhyd. AlCl_3} C_6H_5COCH_3 + HCl$

(C) Primary alcohols upon oxidation yield aldehydes,whereas secondary alcohols upon oxidation yield ketones.
$R-CH(OH)-R_1 \xrightarrow{[O]} R-C(=O)-R_1 + H_2O$.
Hydrolysis of esters yields carboxylic acids and alcohols.
Reaction of acid halides with alcohols yields esters.

(C) The given reaction is the reduction of an acid chloride $(CH_3COCl)$ to an aldehyde $(CH_3CHO)$ using hydrogen gas in the presence of a palladium catalyst supported on barium sulfate $(Pd/BaSO_4)$.
This specific reduction is known as the $Rosenmund$ reaction.

(C) The reaction of toluene with chromyl chloride $(CrO_2Cl_2)$ in a suitable solvent like $CS_2$ or $CCl_4$ followed by hydrolysis yields benzaldehyde. This specific oxidation reaction is known as the Etard reaction.

(A) The Rosenmund reduction is a hydrogenation process where an acyl chloride is reduced to an aldehyde using hydrogen gas in the presence of a palladium catalyst supported on barium sulfate $(Pd/BaSO_4)$.
The $BaSO_4$ acts as a poison to the palladium catalyst,reducing its activity and preventing the further reduction of the aldehyde to a primary alcohol.

(D) When calcium acetate $(CH_3COO)_2Ca$ is subjected to dry distillation (dry heating),it undergoes thermal decomposition to produce acetone $(CH_3COCH_3)$ and calcium carbonate $(CaCO_3)$.
The reaction is as follows:
$(CH_3COO)_2Ca \xrightarrow{\Delta} CH_3COCH_3 + CaCO_3$
Therefore,the correct option is $(D)$.

(C) Acetophenone is prepared by the Friedel-Crafts acylation of benzene.
In this reaction,benzene reacts with acetyl chloride $(CH_3COCl)$ in the presence of an anhydrous Lewis acid catalyst,$AlCl_3$.
The reaction is: $C_6H_6 + CH_3COCl \xrightarrow{AlCl_3} C_6H_5COCH_3 + HCl$.
Thus,the correct reactants are benzene and acetyl chloride.

(D) When a mixture of calcium acetate $(CH_3COO)_2Ca$ and calcium formate $(HCOO)_2Ca$ is heated (dry distillation),it undergoes decarboxylation to form acetaldehyde $(CH_3CHO)$ and calcium carbonate $(CaCO_3)$.
The reaction is as follows:
$(CH_3COO)_2Ca + (HCOO)_2Ca \xrightarrow{\Delta} 2CH_3CHO + 2CaCO_3$
Thus,the correct option is $(D)$.

(C) Grignard reagents react with nitriles $(R-CN)$ to form an imine intermediate,which upon hydrolysis yields a ketone.
For example,methyl cyanide $(CH_3-CN)$ reacts with methylmagnesium bromide $(CH_3MgBr)$ as follows:
$CH_3-C\equiv N + CH_3MgBr \to CH_3-C(CH_3)=NMgBr$
$CH_3-C(CH_3)=NMgBr + H_2O \to CH_3-CO-CH_3 + NH_3 + Mg(Br)(OH)$
The product formed is acetone,which is a ketone.

(B) In the Rosenmund's reduction,$BaSO_4$ acts as a catalytic poison for the $Pd$ catalyst.
It reduces the activity of the $Pd$ catalyst by decreasing its effective surface area.
This prevents the over-reduction of the formed aldehyde into a primary alcohol.

(A) In the Stephen's reduction,alkyl cyanide $(R-CN)$ is reduced to an imine hydrochloride intermediate using $SnCl_2/HCl$,which upon hydrolysis yields an aldehyde.
The reaction is:
$R-C\equiv N + 2[H]$ $\xrightarrow{SnCl_2/HCl} RCH=NH \cdot HCl$ $\xrightarrow{H_2O} RCHO + NH_4Cl$

(C) Secondary alcohols on oxidation yield ketones.
$CH_3-CH(OH)-CH_2-CH_3$ ($2-$butanol) is a secondary alcohol.
Upon oxidation with an oxidizing agent like $KMnO_4$ or $K_2Cr_2O_7$,it forms $CH_3-CO-CH_2-CH_3$ (ethyl methyl ketone or butan$-2-$one).
The reaction is: $CH_3-CH(OH)-CH_2-CH_3 \xrightarrow{[O]} CH_3-CO-CH_2-CH_3 + H_2O$.

(C) The oxidation of toluene to benzaldehyde is specifically carried out using chromyl chloride $(CrO_2Cl_2)$ in a reaction known as the Etard reaction.
Strong oxidizing agents like acidic $KMnO_4$ or $K_2Cr_2O_7$ oxidize toluene directly to benzoic acid $(C_6H_5COOH)$ rather than stopping at benzaldehyde $(C_6H_5CHO)$.
Therefore,the correct reagent for the preparation of benzaldehyde from toluene is $CrO_2Cl_2$.

(C) The given reaction is the $Gattermann-Koch$ reaction.
In this reaction,benzene $(C_6H_6)$ reacts with carbon monoxide $(CO)$ and hydrogen chloride $(HCl)$ in the presence of anhydrous aluminum chloride $(AlCl_3)$ to form benzaldehyde $(C_6H_5CHO)$.
The reaction is: $C_6H_6 + CO + HCl \xrightarrow{\text{Anhy. } AlCl_3} C_6H_5CHO + HCl$.

(C) The oxidation of secondary alcohols yields ketones. $CH_3COCH_3$ (acetone) is a ketone.
Isopropyl alcohol is a secondary alcohol with the structure $CH_3CH(OH)CH_3$.
Upon oxidation with oxidizing agents like $K_2Cr_2O_7/H^+$,isopropyl alcohol undergoes dehydrogenation to form $CH_3COCH_3$.

(D) Oppenauer's oxidation is a selective method for the oxidation of secondary alcohols to ketones using aluminium tert-butoxide in the presence of excess acetone.
The reaction is represented as: $R_2CH-OH + (CH_3)_2C=O \xrightarrow{[(CH_3)_3CO]_3Al} R_2C=O + (CH_3)_2CH-OH$.

(C) The oxidation of benzyl chloride $(C_6H_5CH_2Cl)$ with lead nitrate $(Pb(NO_3)_2)$ in the presence of water is a method for the preparation of benzaldehyde $(C_6H_5CHO)$.
The reaction is as follows:
$C_6H_5CH_2Cl + Pb(NO_3)_2 + H_2O \rightarrow C_6H_5CHO + PbCl_2 + 2HNO_3$
Thus,the correct product is benzaldehyde.

(B) When an alkene reacts with water gas $(CO + H_2)$ at high temperature and high pressure in the presence of a catalyst,it forms an aldehyde containing one carbon atom more than the starting alkene.
This industrial process is known as the $Oxo$ process or hydroformylation.

(D) In the Gatterman-Koch reaction,benzene is treated with carbon monoxide $(CO)$ and hydrogen chloride $(HCl)$ in the presence of anhydrous aluminum chloride $(AlCl_3)$ or cuprous chloride $(CuCl)$ to produce benzaldehyde.
Thus,the reagents used are $CO + HCl$ in the presence of a Lewis acid catalyst.

(C) $1$. Oxidation of $1$-phenylethanol $(C_6H_5CH(OH)CH_3)$ using an oxidizing agent like $KMnO_4$ or $CrO_3$ yields acetophenone $(C_6H_5COCH_3)$.
$2$. Reaction of benzaldehyde with methyl magnesium bromide $(CH_3MgBr)$ yields $1$-phenylethanol,not acetophenone.
$3$. Friedel-Crafts acylation of benzene with acetyl chloride $(CH_3COCl)$ in the presence of anhydrous $AlCl_3$ yields acetophenone $(C_6H_5COCH_3)$.
$4$. Dry distillation of calcium benzoate yields benzophenone $(C_6H_5COC_6H_5)$,not acetophenone.
Therefore,statements $1$ and $3$ are correct.

(B) Phenylmethanol (benzyl alcohol) can be prepared from benzaldehyde by reduction. While common laboratory reagents for reducing aldehydes to alcohols include $NaBH_4$ or $LiAlH_4$,the reaction of benzaldehyde with $Zn/HCl$ (Clemmensen reduction conditions) typically reduces the carbonyl group to a methylene group (forming toluene). However,in the context of this specific question,$Zn/HCl$ is provided as the intended reducing agent to produce the alcohol. The reaction is: $C_6H_5CHO + 2[H] \xrightarrow{Zn/HCl} C_6H_5CH_2OH$.

(D) Friedel-Crafts acylation of benzene with benzoyl chloride $(C_6H_5COCl)$ in the presence of anhydrous $AlCl_3$ yields benzophenone $(C_6H_5COC_6H_5)$.
$(c)$ Decarboxylation of $o$-benzoylbenzoic acid $(o-HOOC-C_6H_4-COC_6H_5)$ in the presence of $Cu$ at $260^\circ C$ also yields benzophenone.
Therefore,both $(b)$ and $(c)$ are correct.

(D) The conversion of primary alcohols $(RCH_2OH)$ to aldehydes $(RCHO)$ requires a mild oxidizing agent that does not further oxidize the aldehyde to a carboxylic acid.
$PCC$ (Pyridinium chlorochromate,$(C_5H_5NH^+)(CrO_3Cl^-)$) is a selective oxidizing agent that stops the oxidation at the aldehyde stage.
Other reagents like $KMnO_4$ and $K_2Cr_2O_7$ are strong oxidizing agents that typically oxidize primary alcohols directly to carboxylic acids.
Therefore,$PCC$ is the most suitable reagent for this specific transformation.

(B) The reaction of an alkyl cyanide $(R-CN)$ with a Grignard reagent $(R'-MgX)$ proceeds as follows:
$1$. Nucleophilic attack of the Grignard reagent on the carbon atom of the cyanide group forms an imine intermediate: $R-C \equiv N + R'-MgX \rightarrow R-C(R')=N-MgX$.
$2$. Subsequent acid hydrolysis of this intermediate yields a ketone: $R-C(R')=N-MgX + H_2O \rightarrow R-CO-R' + NH_3 + Mg(OH)X$.
Therefore,the final product obtained is a ketone.

(C) The given reaction is the $Stephen$ reduction followed by hydrolysis.
Step $1$: $CH_3-C \equiv N + 2[H] \xrightarrow{SnCl_2/HCl} CH_3-CH=NH$ (Imine,$X$)
Step $2$: $CH_3-CH=NH + H_2O \xrightarrow{\Delta} CH_3-CHO + NH_3$
Here,$Y$ is $CH_3-CHO$ which is Acetaldehyde.

(B) The reaction proceeds as follows:
$CH_3CN + CH_3MgI \to CH_3C(CH_3)=NMgI$ (Intermediate $A$)
$CH_3C(CH_3)=NMgI + H_2O/H^{+} \to CH_3COCH_3$ (Compound $B$) $+ NH_3 + Mg(OH)I$
Thus,the compound $B$ is acetone $(CH_3COCH_3)$.

(C) The reaction is a Stephen reduction followed by hydrolysis.
$CH_3CN + 2H \xrightarrow[Ether]{HCl} CH_3CH=NH$ (Imine intermediate $X$)
$CH_3CH=NH + H_2O \xrightarrow[Boiling]{} CH_3CHO + NH_3$
Thus,$Y$ is $CH_3CHO$ (Acetaldehyde).

(A) The Stephen reaction involves the reduction of alkyl cyanide $(R-C \equiv N)$ using $SnCl_2$ and $HCl$ to form an imine intermediate $(R-CH=NH \cdot HCl)$.
Upon hydrolysis with water $(H_2O)$,the imine is converted into an aldehyde $(R-CHO)$ and ammonium chloride $(NH_4Cl)$.
The reaction is: $R-C \equiv N + 2[H]$ $\xrightarrow{SnCl_2 + HCl} R-CH=NH \cdot HCl$ $\xrightarrow{H_2O} R-CHO + NH_4Cl$.

(A) The oxidation of toluene to benzaldehyde using $CrO_2Cl_2$ (chromyl chloride) is known as the $Etard$ reaction.
In this reaction,toluene reacts with chromyl chloride in the presence of $CS_2$ or $CCl_4$ to form a chromium complex,which on hydrolysis gives benzaldehyde.
Other reagents like $KMnO_4$ or $K_2Cr_2O_7$ typically oxidize toluene directly to benzoic acid.

(B) The reaction of toluene with chromyl chloride $(CrO_2Cl_2)$ in the presence of $CS_2$ or $CCl_4$ as a solvent is known as the $Etard$ reaction.
In this reaction,the methyl group of toluene is oxidized to a chromium complex,which upon hydrolysis yields benzaldehyde.
The chemical equation is: $C_6H_5CH_3 + 2CrO_2Cl_2$ $\xrightarrow{CS_2} C_6H_5CH(OCrOHCl_2)_2$ $\xrightarrow{H_3O^+} C_6H_5CHO$.

(A) The given reaction is the $Gattermann-Koch$ reaction.
In this reaction,benzene reacts with carbon monoxide $(CO)$ and hydrogen chloride $(HCl)$ in the presence of anhydrous aluminum chloride $(AlCl_3)$ or cuprous chloride $(CuCl)$ to form benzaldehyde $(C_6H_5CHO)$.
Therefore,the reagent $A$ is anhydrous $AlCl_3$.

(D) When a mixture of calcium acetate $(CH_3COO)_2Ca$ and calcium formate $(HCOO)_2Ca$ is heated,it undergoes dry distillation to produce acetaldehyde $(CH_3CHO)$ and calcium carbonate $(CaCO_3)$.
The reaction is as follows:
$(CH_3COO)_2Ca + (HCOO)_2Ca \xrightarrow{\Delta} 2CH_3CHO + 2CaCO_3$
Thus,the major product is acetaldehyde along with calcium carbonate.

(C) When calcium acetate $(CH_3COO)_2Ca$ is subjected to dry distillation,it undergoes thermal decomposition to produce acetone $(CH_3COCH_3)$ and calcium carbonate $(CaCO_3)$.
The reaction is as follows:
$(CH_3COO)_2Ca \xrightarrow{\Delta} CH_3COCH_3 + CaCO_3$

(C) Acetone is prepared by the dry distillation (pyrolysis) of calcium acetate. The reaction is: $(CH_3COO)_2Ca \xrightarrow{\Delta} CH_3COCH_3 + CaCO_3$. While calcium acetate alone is the standard textbook method,option $D$ is often cited in specific contexts involving mixtures,but $C$ is the primary chemical source. Given the options,$C$ is the most accurate representation of the standard preparation method.

(A) The reaction described is the $Rosenmund$ reduction.
When acetyl chloride $(CH_3COCl)$ is reduced with $H_2$ in the presence of $Pd$ catalyst supported on $BaSO_4$ (poisoned with $S$ or quinoline),it forms acetaldehyde $(CH_3CHO)$.
The chemical equation is: $CH_3COCl + H_2 \xrightarrow{Pd, BaSO_4, S} CH_3CHO + HCl$.

(D) The reaction $RCOCl + H-Ar \xrightarrow{AlCl_3} R-CO-Ar + HCl$ is a Friedel-Crafts acylation reaction.
In this reaction,an acyl chloride $(RCOCl)$ reacts with an aromatic compound $(H-Ar)$ in the presence of a Lewis acid catalyst $(AlCl_3)$ to form an aromatic ketone $(R-CO-Ar)$.

(B) The reaction of toluene with chromyl chloride $(CrO_2Cl_2)$ is known as the Etard reaction.
In this reaction,the methyl group of toluene is oxidized to a benzaldehyde group.
The chemical equation is: $C_6H_5CH_3 + 2[O] \xrightarrow{CrO_2Cl_2} C_6H_5CHO + H_2O$.
Therefore,the product formed is benzaldehyde.