Write a test to detect the presence of double bond in a molecule.
Presence of double bond in a molecule is detected by following two methods:
(i) $\mathrm{Br}_2$ in $\mathrm{CCl}_4$ test ${\mathrm{When} \mathrm{Br}_2 / \mathrm{CC}_4}^2$ is added unsaturated compound then orange colour of bromine disappears and dibromoderivative is formed. (colourless).
(ii) Bayer's test When alkaline solution of $\mathrm{KMnO}_4$ is added to the solution of unsaturated compound then its pink colour disappears due to the formation of dihydroxy derivative.
Diphenyls are potential threat to the environment. How are these produced from aryl halides?
In environment, diphenyl is formed during the incomplete combustion of mineral oil and coal. It is present in the exhaust gases of vehicles and in exhaust air from residential and industrial heating devices.
Acute exposure to high levels of biphenyl has been observed to cause eye and skin irritation and toxic effects on the liver, kidneys and central /peripheral nervous system. Kidneys of animals are also affected due to the ingestion of biphenyls. In rats, fetofoxicity has been oserved if they are exposed to high levels of biphenyl.
Preparation of diphenyls from aryl halides
Aryl halides, when treated with sodium in dry ether give diphenyl. This reaction is named as Fittig reaction.
What are the IUPAC names of the insecticide DDT and benzene hexachloride? Why is their use banned in India and other countries?
The IUPAC name of DDT is 2,2-bis (4-chlorophenyl)-1,1,1-trichloroethane and that of benzene hexachloride is 1,2,3,4,5,6-hexachlorocyclohexane.
They are banned in india because they are non-biodegradable. Instead, they get deposited and stored in fatty tissues. If this ingestion continues at a steady rate, DDT builds up within the animal over time. This will affects the reproductive system of animals.
If animals including humans are exposed to high levels of benzene hexachloride then it may cause acute poisoning. Apart from that this BHC may affect liver functioning in humans.
Elimination reactions (especially $\beta$-elimination) are as common as the nucleophilic substitution reaction in case of alkyl halides. Specify the reagents used in both cases.
Elimination reactions are as common as the nucleophilic substitution reaction in case of alkyl halides as two reactions occur simultaneously. Generally, at lower temperature and by using weaker base nucleophilic substitution reaction occur while at higher temperature and by using a stronger base elimination reactions (especially $\beta$ - elimination) take place. e.g., If ethyl bromide is treated with aq. KOH , at low temperature it gives ethanol while if it is treated with alc, KOH at high temperature then it gives ethene.
$\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Br} \xrightarrow[373 \mathrm{~K}]{\text { Aq. } \mathrm{KOH}} \underset{\substack{\text { Ethanol }}}{\mathrm{CH}_2 \mathrm{CH}_2 \mathrm{OH}}$ (Nucleophilic substitution reaction)
$\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Br} \xrightarrow[473-523 \mathrm{~K}]{\mathrm{Alc} \mathrm{KOH}} \underset{\text { Ethene }}{\mathrm{CH}_2=\mathrm{CH}_2}$ (Elimination reaction)
How will you obtain monobromobenzene from aniline?
When aniline, dissolved or suspended in cold aqueous mineral acid, is treated with sodium nitrite, a diazonium salt is formed. This diazo salt on treatment with cuprous bromide gives monobromobenzene.
This reaction is named as Sandmeyer's reaction. If benzene diazonium chloride is treated with copper in HBr then the product formed is bromobenzene. This reaction is known as Gattermann reaction.