Organic Chemistry Answers

This question concerns the aromatic hydrocarbon benzene, which contains a delocalised system of eelectrons.

• Cite 3 pieces of evidence that benzene does in fact contain such a system, rather than a system of alternating single and double bonds.
• What do you understand by the term "delocalised system"?

Benzyl alcohol (C₆H₅CH₂OH) and benzoic acid may be obtained from benzaldehyde by the reaction with potassium hydroxide, using the method described below.

Benzaldehyde (26.5g) was added to a concentrated solution of potassium hydroxide in a corked bottle. The mixture was shaken and allowed to stand for several hours. Water was added and the mixture extracted with two separate portions of ether. The ether extracts were combined, dried, and distilled to give a liquid product A. The aqueous layer was acidified with concentrated hydrochloric acid and the white precipitate B filtered off by suction and purified. 10g of product A and 12g of product B were formed.

1. Calculate the percentage yield of B.
2. Sketch the apparatus you would have used for:

(i) Carrying out the ether extraction

(ii) Filtering off the product B.

Question:

Benzyl alcohol (C₆H₅CH₂OH) and benzoic acid may be obtained from benzaldehyde by the reaction with potassium hydroxide, using the method described below.

Benzaldehyde (26.5g) was added to a concentrated solution of potassium hydroxide in a corked bottle. The mixture was shaken and allowed to stand for several hours. Water was added and the mixture extracted with two separate portions of ether. The ether extracts were combined, dried, and distilled to give a liquid product A. The aqueous layer was acidified with concentrated hydrochloric acid and the white precipitate B filtered off by suction and purified. 10g of product A and 12g of product B were formed.

(a) Why were 2 separate portions of ether used rather than one large one?

(b) How would you have dried the ether solution?

(c) How would you purify B and how would you confirm its purity?

100 mL of a water sample required 25 mL of N/50 H₂SO₄ for neutralization to phenolphthalein end point. After this, methyl orange indicator was added and further acid required was again 25 mL Calculate type and extent of alkalinity.

Question:

Benzyl alcohol (C₆H₅CH₂OH) and benzoic acid may be obtained from benzaldehyde by the reaction with potassium hydroxide, using the method described below.

Benzaldehyde (26.5g) was added to a concentrated solution of potassium hydroxide in a corked bottle. The mixture was shaken and allowed to stand for several hours. Water was added and the mixture extracted with two separate portions of ether. The ether extracts were combined, dried, and distilled to give a liquid product A. The aqueous layer was acidified with concentrated hydrochloric acid and the white precipitate B filtered off by suction and purified. 10g of product A and 12g of product B were formed.

(a) Why were 2 separate portions of ether used rather than one large one?

(b) How would you have dried the ether solution?

(c) How would you purify B and how would you confirm its purity?

Benzyl alcohol (C₆H₅CH₂OH) and benzoic acid may be obtained from benzaldehyde by the reaction with potassium hydroxide, using the method described below.

Benzaldehyde (26.5g) was added to a concentrated solution of potassium hydroxide in a corked bottle. The mixture was shaken and allowed to stand for several hours. Water was added and the mixture extracted with two separate portions of ether. The ether extracts were combined, dried and distilled to give a liquid product A. The aqueous layer was acidified with concentrated hydrochloric acid and the white precipitate B filtered off by suction and purified. 10g of product A and 12g of product B were formed.

(a) Which of the two product A & B is benzyl alcohol? Write an equation for the reaction of benzaldehyde with potassium hydroxide and comment on the nature of this reaction.

(b) Why do you think water was added to the reaction mixture before the extraction with ether?

1.09g of a monobromoalkane, A that is immiscible with water was refluxed with excess aqueous sodium hydroxide. The liquid A was dissolved and the resulting solution was neutralized with nitric acid. Excess silver nitrate solution was added and a precipitate of silver bromide was formed. The precipitate was filtered, washed & dried. The precipitate weighed 1.99g.

The filtrate was distilled and a high boiling point liquid B was obtained. b contained 52.2% carbon, 13% hydrogen, and 34.8% oxygen by mass.

C = 12 H = 1 O = 16, Br = 80 Ag = 108

(a) How many moles of A are contained in 1.09g? Explain or show clearly how you arrived at your answer

(b) Determine the molecular formula of B

(c) Name compounds A & B

1.09g of a monobromoalkane, A that is immiscible with water was refluxed with excess aqueous sodium hydroxide. The liquid A was dissolved and the resulting solution was neutralized with nitric acid. Excess silver nitrate solution was added and a precipitate of silver bromide was formed. The precipitate was filtered, washed & dried. The precipitate weighed 1.99g.

The filtrate was distillled and a high boling point liquid B was obtained. b contained 52.2% carbon, 13% hydrogen and 34.8% oxygen by mass.

C = 12 H = 1 O = 16, Br = 80 Ag = 108

(a) Sketch a reflux apparatus

(b) Why was the solution not neutralised with hydrochloric acid?

(c) Write equations for the reaction taking place.

Given that A = 1, 2-dibromopropane

How would you convert B into its corresponding alcohol?

Give a mechanism for the reaction

Give the structures of:

A. 1, 2-dibromopropane

B. 2-methyl-2-chloro ethane

How would you obtain A from propene? Give a mechanism for the reaction