Nitrogen Compounds: Chemistry 9701 (Cambridge International AS & A Level)

A student has a bottle of 1-chlorobutane, $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{Cl}$, and uses it to make two different nitrogen-containing products.

(a) The student heats 1-chlorobutane under pressure in a sealed tube with a large excess of ammonia, $\text{NH}_3$, dissolved in ethanol. State the type of mechanism involved, and give the structural formula and name of the main organic product formed. [3]

(b) In a separate experiment, the student instead heats 1-chlorobutane under reflux with potassium cyanide, KCN, dissolved in ethanol. Give the structural formula and name of the organic product formed. [2]

(c) The nitrile from part (b) is heated under reflux with dilute hydrochloric acid to hydrolyse it. Give the structural formula and name of the carboxylic acid formed, and explain why this carboxylic acid has one more carbon atom than the amine formed in part (a), even though both were made from the same starting halogenoalkane. [3]

Pentan-3-one, $\text{CH}_3\text{CH}_2\text{COCH}_2\text{CH}_3$, is warmed with hydrogen cyanide in the presence of a trace of potassium cyanide as catalyst.

What is the structural formula of the organic product formed?

Aqueous solutions of ammonia, methylamine and phenylamine are compared.

(a) Explain what is meant by describing methylamine as a Brønsted-Lowry base, referring to the nitrogen lone pair, and write an equation for the reaction of methylamine with water. [3]

(b) Place ammonia and methylamine in order of increasing base strength, and explain why methylamine is the stronger base of the two. [3]

(c) Phenylamine is a much weaker base than ammonia. Explain this difference, referring to the nitrogen lone pair and the benzene ring in phenylamine. [3]

Methylamine, $\text{CH}_3\text{NH}_2$, is reacted with propanoyl chloride, $\text{CH}_3\text{CH}_2\text{COCl}$, at room temperature.

(a) Give an equation for this reaction, and name the amide formed. [2]

(b) State and explain why this amide is a much weaker base than methylamine. [3]

(c) The amide is then heated under reflux with dilute hydrochloric acid. Give the structural formulae of the two products formed in this hydrolysis. [2]

An amino acid, 2-aminobutanoic acid, has the structural formula $\text{CH}_3\text{CH}_2\text{CH(NH}_2\text{)COOH}$.

(a) Give the structural formula of the zwitterion of 2-aminobutanoic acid, and state the type of intramolecular process that produces it from the structure shown above. [2]

(b) 2-Aminobutanoic acid reacts with glycine, $\text{H}_2\text{NCH}_2\text{COOH}$, so that the carboxylic acid group of 2-aminobutanoic acid condenses with the amine group of glycine. Give the structural formula of the dipeptide formed, name the type of bond created, and give the formula of the small molecule lost. [3]

(c) A sample of this dipeptide is placed in a buffer solution at a pH well above its isoelectric point and subjected to electrophoresis. State, with a reason, the overall charge on the dipeptide under these conditions and the electrode towards which it will migrate. [2]

Propanenitrile, $\text{CH}_3\text{CH}_2\text{CN}$, is reduced using an excess of lithium aluminium hydride, $\text{LiAlH}_4$, in dry ether, followed by addition of dilute acid on work-up.

What is the structural formula of the organic product formed?

Phenylamine, $\text{C}_6\text{H}_5\text{NH}_2$, is prepared from nitrobenzene and then converted into an azo dye.

(a) Nitrobenzene, $\text{C}_6\text{H}_5\text{NO}_2$, is heated under reflux with tin and an excess of concentrated hydrochloric acid, and the mixture is then treated with excess sodium hydroxide solution. Give an overall equation for the reduction (using $[\text{H}]$ to represent hydrogen from the reducing agent), and state the purpose of adding the sodium hydroxide solution. [3]

(b) The phenylamine obtained in (a) is treated with nitrous acid, $\text{HNO}_2$ (generated in situ from sodium nitrite and dilute hydrochloric acid), at a temperature kept below $10\,^\circ\text{C}$. Give an equation for this reaction, name the type of reaction and the organic product formed, and explain why the temperature must be kept below $10\,^\circ\text{C}$. [3]

(c) The cold solution from (b) is added to an alkaline solution of phenol. State what is observed, give the structural formula of the azo compound formed (coupling occurs at the position on the phenol ring para to the -OH group), and explain why this compound is coloured. [3]

Ethylamine, $\text{CH}_3\text{CH}_2\text{NH}_2$, is used in two separate experiments.

(a) In the first experiment, an excess of ethylamine is added to dilute hydrochloric acid. Give an equation for this reaction, name the salt formed, and explain, in terms of the nitrogen atom, why ethylamine reacts in this way. [3]

(b) In the second experiment, a limited amount of bromoethane, $\text{CH}_3\text{CH}_2\text{Br}$, is added to an excess of ethylamine dissolved in ethanol. Give an equation for the main organic reaction taking place, name the type of mechanism, and give the name of the organic product formed. [3]

(c) If a large excess of bromoethane were used instead in (b), the product could react further, eventually forming a quaternary ammonium salt. Explain, in terms of the nitrogen lone pair, why this further reaction is possible. [2]

Alanine, $\text{CH}_3\text{CH(NH}_2\text{)COOH}$, has an isoelectric point of approximately pH 6. A solution of alanine is adjusted to pH 1, a pH well below its isoelectric point, using dilute hydrochloric acid.

What is the predominant form of alanine present at pH 1, and towards which electrode would it migrate during electrophoresis?

The dipeptide glycylalanine, $\text{H}_2\text{NCH}_2\text{CONHCH(CH}_3\text{)COOH}$, is heated under reflux with an excess of concentrated hydrochloric acid until hydrolysis is complete.

(a) Name the type of reaction taking place, and give the structural formulas of the two products formed, showing each one in the form in which it would predominantly exist in this strongly acidic solution. [4]

(b) State what is meant by the isoelectric point of an amino acid, and explain why glycine, held in a buffer solution at its isoelectric point, does not migrate towards either electrode during electrophoresis. [3]