Tag: reactions of haloarenes

Questions Related to reactions of haloarenes

The order of reactivities of methyl halides in the formation of Grignard reagent is :

reactions of haloarenes haloalkanes and haloarenes chemistry

  1. $CH _3I> CH _3Br> CH _3Cl$

  2. $CH _3Cl> CH _3Br> CH _3I$

  3. $CH _3Br> CH _3Cl> CH _3I$

  4. $CH _3Br> CH _3I> CH _3Cl$

Show answer
Correct Option: A
Explanation:

Grignard reagents are highly reactive and react with any source of a proton to give hydrocarbons. Water, alcohol, amines are sufficiently acidic to convert them to corresponding hydrocarbons. Halide reactivity increases in the order $Cl < Br < I$

Therefore A is the correct option. 

Grignard reagent, a very useful starting compound for a number of organic reaction can be prepared by:

reactions of haloarenes haloalkanes and haloarenes chemistry

  1. reaction of alkyl halides with a solution of magnesium hydroxide

  2. reaction of alkyl halide with dry magnesium powder in presence of dry ether

  3. reaction of $MgCl _2$ with ether and alcohol

  4. rection of alkyl halide with magnesium in presence of alcohol

Show answer
Correct Option: B
Explanation:

$R-X+Mg\xrightarrow{dryether} R-Mg-X$
                                        grignard reagent

In the depression of freezing point experiment, it is found that
(i) The vapour pressure of the solution is less than that of pure solvent
(ii) The vapour pressure of the solution is more than that of pure solvent
(iii) Only solute molecules solidify at the freezing point
(iv) Only solvent molecules solidify at the freezing point

reactions of haloarenes haloalkanes and haloarenes chemistry

  1. I,II

  2. II,III

  3. I,IV

  4. I,II,III

Show answer
Correct Option: C

Which one of the following would not be a suitable solvent for Grignard reagent?

reactions of haloarenes haloalkanes and haloarenes chemistry

  1. $CH _{3}CH _{2}OCH _{2}CH _{3}$, diethylether

  2. tetrahydrofuran (THF)

  3. $CH _{3}CH _{2}OH$, ethanol

  4. They would all be suitable solvent.

Show answer
Correct Option: C
Explanation:

Ethanol has acidic hydrogen, when we use ethanol as solvent it will react with grignard reagent, so it cannot be used as solvent in grignard synthesis. 

Ullmann reaction involves the use of the following reactants:

reactions of haloarenes haloalkanes and haloarenes chemistry

  1. iodobenzene and sodium

  2. benzene and copper

  3. iodobenzene and copper powder

  4. benzene diazonium chloride and $Cu/HCl$

Show answer
Correct Option: C
Explanation:

Statemetn (c) is Ullmann reaction
$2ArI+Cu\longrightarrow Ar-Ar+Cu{I} _{2}$

The interaction of elemental sulphur with Grignard reagent gives ......... .

reactions of haloarenes haloalkanes and haloarenes chemistry

  1. $H _2S$ gas

  2. Mercaptan

  3. thioalcohol

  4. $R-S-OH$

Show answer
Correct Option: B,C
Explanation:

The interaction of elemental sulphur $(S)$ with grignard reagent $(RMgX)$ gives mercaptan $(RSH)$ which is also called thioalcohol.

Acetyl bromide reacts with excess of $CH _3MgI$ followed by treatment with a saturated solution of $NH _4Cl$ gives:

reactions of haloarenes haloalkanes and haloarenes chemistry

  1. acetone

  2. acetamide

  3. $2$-Methyl-$2$-propanone

  4. acetyl iodide

Show answer
Correct Option: C
Explanation:

C. $2$-methyl-$2$-propanol
Acetyl chloride reacts with two equivalents of Grignard reagent to form tertiary alcohol, two of the groups bonded to $C$ having $O$H group are from the Grignard reagent.

The acid that cannot be prepared by Grignard reagent is.

reactions of haloarenes haloalkanes and haloarenes chemistry

  1. Acetic acid

  2. Formic acid

  3. Butyric acid

  4. Benzoic acid

Show answer
Correct Option: B
Explanation:

Formic acid (containing only one C atom) cannot be prepared by Grignard reagent. The acid that can be prepared by Grignard reagent should contain a minimum of two carbon atoms. An example is as shown below.
$\displaystyle CO _2+CH _3-MgI \rightarrow CH _3-COO-MgI \xrightarrow [hydrolysis]{H^+} CH _3-COOH+ Mg(I)OH$

Grignard reagent is usually prepared by :

$R-X+Mg\xrightarrow {E{ t } _{ 2 }O} RMgX$               Grignard reagent

$Ar-X+Mg\xrightarrow {E{ t } _{ 2 }O} ArMgX$           Grignard reagent

Grignard reagent acts as a strong base. Grignard reagent carry out nucleophilic attack in absence of acidic hydrogen. Grignard reagent form complex with its ether solvent. Complex formation with molecule of ether is an important factor in the formation and stability of Grignard reagent.

Which of the following Grignard reagents are not possible ?

reactions of haloarenes haloalkanes and haloarenes chemistry

  1. $HS - CH _{2} - CH _{2} - CH _{2}MgBr$

  2. $HO - CH _{2} - CH _{2} - CH _{2}MgBr$

  3. $NH _{2} - CH _{2} - CH _{2} - CH _{2}MgBr$

  4. All of these

Show answer
Correct Option: D
Explanation:

(A)$\overset {\delta +}{H}-S-CH _2CH _2CH _2-MgBr \xrightarrow [reaction]{acid-base} BrMgS-CH _2CH _2CH _3$


(B) $H-O-CH _2CH _2CH _2MgBr \xrightarrow [reaction]{acid-base} BrMgO-CH _2CH _2CH _3$


(C) $\overset {\delta +}{H}-\underset {|}{N}-CH _2CH _2-CH _2-MgBr \xrightarrow [reaction]{acid-base} BrMg-\underset {|}{N}-CH _2CH _2CH _3$
         $\delta^+ H$                                                                                        $H$

So, all of these Grignard reagent can take their own acidic hydrogen. Therefore all of these Grignard reagents are not possible.

A student was carrying out a Grignard reaction between $PhMgBr$ and ethyl benzoate. She ran out of anhydrous ether just after the Grignard reagent was made. Which of the following solvents can still used to dissolve the ethyl benzoate for its reaction with already formed $PhMgBr$

reactions of haloarenes haloalkanes and haloarenes chemistry

  1. acetone

  2. ethyl acetate

  3. absolute alcohol

  4. benzene

Show answer
Correct Option: D
Explanation:

Solution:- (D) benzene

Grignard reagent contains $R$-group which does nucleophilic addition on acetone and accepts Proton from alcohol.
Thus non polar benzene should be taken to carry out above reaction.