KA 3: synthesis 2

Question 1

what are alcohols?

Answer 1

substituted alkanes in which one or more of the hydrogen atoms is replaced with a hydroxyl functional group

Question 2

how can alcohols be prepared?

Answer 2

-haloalkanes by substitution

-alkenes by acid-catalysed hydration (addition)

-aldehydes and ketones by reduction using a reducing agent such as lithium aluminium hydride

-fermentation of sugars

Question 3

describe the preparation of alcohls:

aldehydes and ketones by reaction with lithium aluminium hydride in ethoxyethane

Answer 3

reduction of aldehyde=> primary alochol

reduction of ketone=> secondary alcohol

-the reagent for this is LiAlH4

Question 4

list the reactions of alcohols

Answer 4

-dehydration to form alkenes using aluminium oxide, conc sulf acid or conc phos acid

-oxidation of primary alcohols to form aldehydes and then carboxylic acids and secondary alcohols to form ketones, using
acidified permanganate, acidified dichromate or hot copper(II) oxide

-formation of alcoholic alkoxides by reaction with some reactive metals such as potassium or sodium, which can then be reacted with monohaloalkanes to form ethers

-formation of esters by reaction with carboxylic acids using concentrated sulfuric acid or concentrated phosphoric acid as a catalyst

-formation of esters by reaction with acid chlorides this gives a faster reaction than reaction with carboxylic acids, and no catalyst is needed

Question 5

what explains the properties of alcohols?

Answer 5

-hydroxyl groups make alcohols polar, which gives rise to hydrogen bonding

Question 6

what are ethers?

Answer 6

substituted alkanes. the alkoxy group is named by adding the ending “oxy” to the alkyl substituent

Question 7

how can ethers be prepared

Answer 7

a nucleophilic substitution reaction by reacting a monoalkane with an alkoxide

Question 8

why do ethers have lower boiling points than alcohols?

Answer 8

due to the lack of hydrogen bonding between ether molecules

Question 9

methoxymethane and methoxyethane are…

Answer 9

soluble in water

Question 10

why are larger ethers insoluble in water?

Answer 10

due to theit increased molecular size

Question 11

why are ethers commonly used as solvents?

Answer 11

they’re relatively inert chemically and will dissolve many organic compounds

Question 12

how can carboxylic acids be prepared?

Answer 12

-oxidising primary alcohols using acidified potassium permanganate, acidified dichromate and hot copper (II) oxide

-oxidising aldehydes using acidified permangante, acidified dichromate, Fehling’s solution and Tollen’s reagent

-hydrolysing nitriles, esters or amides

Question 13

list the reactions of carboxylic acids

Answer 13

-formation of salts by reactions with metals or bases

-condensation reactions with alcohols to form esters in the presence of concentrated sulfuric or concentrated phosphoric acid

-reaction with amines to form alkylammonium salts that form amides when heated

-reduction with lithium aluminium hydride to form primary alcohols

Question 14

what are amines?

Answer 14

theyre based on a molecule of ammonia where one or more hydrogens have been replaced by an alkyl or aryl group

Question 15

what do amines react with and what do they form

Answer 15

acids to form salts

Question 16

what do primary and secondary amines, but not tertiary amines, display? And what does this results in?

Answer 16

-hydrogn bonding

-primary and secondary amines have higher boiling points than tertiary amines

Question 17

what can primary, secondary and tertiary amine molecules hydrogen bond with? And what does this explain?

Answer 17

-water

-the appreciable solubility of the shorter chain length amines in water

Question 18

Amines, like ammonia, are…

Answer 18

weak bases and dissociate to a slight extent in a an aqueous solution.

the nitrogen atom has a lone pair of electrons which can accept a proton from water, producing hydroxide ions