Unit 3) SYNTHESIS carboxylic acids and amines

Question 1

carboxylic acids contain the functional group…

Answer 1

carboxyl functional group (COOH)

Question 2

short chain carboxylic acids are very ____ in water

why?

Answer 2

• soluble

- due to them having polar carbonyl and hydroxyl groups which can form hydrogen bonds in water.

Question 3

as the non polar hydrocarbon chain length increases , solubility in water _____

Answer 3

decreases

Question 4

carboxylic acids are isomers of _____

Answer 4

esters

Question 5

how can carboxylic acids be prepared

Answer 5

• oxidising primary alcohols or aldehydes
• hydrolysing nitriles
• hydrolysing esters
• hydrolysing amides

Question 6

oxidising primary alcohols

- what do you use

Answer 6

using acidified permanganate, acidified dichromate and hot copper(II) oxide
- alcohols have OH , oxidisng them adds the double bond O

Question 7

oxidising aldehydes

- what do you use

Answer 7

using acidified permanganate, acidified dichromate, Fehling’s solution and Tollens’ reagent
- aldehydes have COH, oxidising them adds a single bonded O

Question 8

hydrolysing nitriles

- what happens and what catalyst is used

Answer 8

• the nitrile is heated under reflux with an aq acid (h3o+) and undergoes hydrolysis
• the hydronium ions of the acid catalyse the reaction

Question 9

hydrolysing esters

• what happens
• what catalyst is used

Answer 9

• the ester undergoes hydrolysis when heated under reflux with an aqueous acid as a catalyst or using an aqueous alkali
• when an alkali is used eg KOH , it shifts the equilibrium to the right , as it reacts with the carboxylic acid (the cooh)

Question 10

hydrolysing amides

Answer 10

• the amide is heated under reflux with an aquous acid or an aquous alkali as catalyst and undergoes hydrolysis
• as with the hydrolysis of esters, usuing an alklai pushes the equilibrium position to the right

Question 11

carboxylic acids behave as typical acids and form salts on reaction with…

Answer 11

• metal oxides - forming carboxylate salt and water
• metal carbonates - forming carboxylate salt , water and carbon dioxide
• alkalis -forming salt and water (this is a neutralisation reaction)

Question 12

what else to carboxylic acids react with

Answer 12

• react with alcohols to form esters
• amines to form amides
• lithium aluminium hydride in ether to form primary alcohols

Question 13

carboxylic acids reacting with alcohols

• what does it form
• what kind of reaction is this
• catalysed by

Answer 13

• forms ester
• condensation
• catalysed by concentrated sulfuric acid or concentrated phosphoric acid

Question 14

carboxylic acids reacting with amines

- forms what

Answer 14

• forms alkylammonium salts , which on heating then forms amides

Question 15

carboxylic acids reacting with lithium aluminium hydride (LiAlH4) in ether

• forms what
• what kind of reaction is this

Answer 15

• forms primary alcohols
• this is a reduction reaction and the LiAlH4 is such a strong reducing agent that it reduces the carboxylic acid directly to the primary alcohol

Question 16

what are amines

Answer 16

organic derivatives of ammonia, in which one or more hydrogen atoms in ammonia has been replaced by by alkyl groups

Question 17

classification of amines

Answer 17

primary - 1 alkyl group attached
secondary - 2 alkyl groups attached
tertiary - 2 alkyl groups attached

Question 18

naming amines

Answer 18

look in notes

Question 19

why do primary and secondary amines have higher boiling points than tertiary amines

Answer 19

• primary and secondary amines have a polar n-h bond, and so have hydrogen bonds between their molecules. tertiary amines cant do this, as they don’t have a hydrogen directly connected to the highly electronegative nitrogen atom

Question 20

why are amines, with low molecular mass soluble in water

Answer 20

they can form hydrogen bonds with water molecules , this is even true for tertiary amines

Question 21

amines are…

Answer 21

weak bases

Question 22

how can amines form dative covalent bonds

Answer 22

the lone pair of electrons on the nitrogen atom of ammonia and amines can accept a proton , forming a dative covalent bond

Question 23

• what happens when amines react with water

- where does equilibrium lie

Answer 23

• forms an alkaline solution with a low concentration of hydroxide ions
• when amines react with water , they dissociate slightly in aqueous solution. They accept a hydrogen ion from water to produce an alkylammonium ion and a hydroxide ion
• an equilibrium is set up and the equilibrium position lies on the left hand side

Question 24

basicity of aliphatic amines depends upon the availability of the lone pair on the ____ atom which is used to bond with the proton

Answer 24

nitrogen

Question 25

how can the relative strengths of amines be compared

Answer 25

by looking at pka values on page 13 of data booklet- the stronger the base the higher the pka value

Question 26

amines increase in base strength as …

Answer 26

as the number of groups attached to the nitrogen increases ( alkly groups are electron donating so there is more electron density on the nitrogen atom. as a result the lone pair is more available to accept a proton )

Question 27

aminobenzene is a weaker base than ammonia- why

Answer 27

as the non bonding electrons become delocalised around the ring