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chem unit 4 > 4.4 Aldehydes and Ketones > Flashcards

4.4 Aldehydes and Ketones Flashcards

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1
Q

Type of rctn alcohols undergo to for aldehydes and ketones

A

Oxidation

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2
Q

How can you tell whether the oxidation of an alcohol will produce an aldehyde or ketone?

A

Primary alcohol will form an aldehyde when oxidised
Secondary alcohol will form a ketone when oxidised

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3
Q

Why is immediate distillation req for the oxidation of an alcohol to an aldehyde

A

Aldehyde must be distilled off immediately as it will undergo further oxidation producing a carboxylic acid

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4
Q

Common oxidising agent in oxidation of alcohols

A

Acidified Potassium dichromate (VI)

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5
Q

Observations when alcohol udergoes oxidation by acidified potassium dichromate (VI)

A

Orange dichromate(VI) ion Cr2O72- is reduced to green chromium(III) ion Cr3+

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6
Q

Observation when acidified potassium dichromate is added to a tertiary alcohol?

A

Solution will remain orange as acidified potassium dichromate (VI) does not react with tertiary alcohols as they can not be oxidised

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7
Q

Chemical eqn for the oxidation of porpan-2-ol to propanone

A

CH3CH(OH)CH3 + [O] -> CH3COCH3 + H2O

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8
Q

Chemical eqn for the oxidation of ethanol to ethanal

A

CH3CH2OH + [O] -> CH3CHO + H2O

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9
Q

Two reagents used to distinguish between aldheydes and ketones

A

Tollen’s reagent
Fehling’s reagent

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10
Q

How can Tollen’s reagent be used to determine whether you have an aldehyde or a ketone?

A

Tollen’s reagent forms a silver mirror on test tude only when warmed with an aldehyde not a ketone

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11
Q

How can Fehling’s reagent be used to determine whether you have an aldehyde or a ketone?

A

Fehling’s reagent is blue, if added to an aldehyde the blue solution will for a brick red ppt, if added to a ketone remains blue

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12
Q

Type of reaction aldehydes and ketones undergo to form alcohols

A

Reduction

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13
Q

Classification of the alcohols formed by reduction of aldehydes and ketones

A

aldehydes will be reduced to a primary alcohol
ketones will be reduced to a secondary alcohol

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14
Q

Common reducing agent used in reduction of aldehydes and ketones to alcohols

A

NaBH4 dissolved in water with methanol

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15
Q

Chemical eqn for the reduction of butanone to butan2ol

A

CH3COCH2CH3 + 2[H] -> CH3C(OH)HCH2CH3

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16
Q

Mechanism for the reduction of propanal to propan-1-ol

A

nucleophilic addition

17
Q

Give the reactants and conditions req for formation of a hydroxynitrile from an aldehyde/ketone

A

Potassium or sodium cyanide added to sulfuric acid to produce hydrogen cyanide at temperature 20C

18
Q

Why is hydrogen cyanide not added directly to an aldehyde/ketone for a nucleophilic addition rctn?

A

HCN is a toxic gas which is hard to store

19
Q

Draw and name mechanism for thr formation of 2-hydroxypropnenitrile from ethanal and hydrogen cyanide

A

Nucleophilic addition

lone pair on C of cyanide ion attacks C polar double bond O intermediate lone pair on O- attacks H+ as cyanide ion w triple bond has joined on end alcohol grp where O was and Ctriple bond N grp attached to carbon

20
Q

Why are hydroxynitriles important?

A

Hydroxynitriles can be hydrolysed to form hydroxy acids which are very useful and are commonly used in the cosmetics industry

21
Q

How does the addition of HCN to ethanal affect the C-C chain length?

A

The C-C chain length will increase by one carbon atom due to the carbon atom in the cyanide ion CN-

22
Q

Structural formula of 2,4-DNP

A

benzene ring with two NO2s at1&3pos a N with a NH2 and H coming off it at 6pos

23
Q

Type of rctn taking place when aldehydes and ketones react with 2,4-DNP

A

Nucleophilic addition-elimination reaction (condensation reaction)

24
Q

How can 2,4-DNP be used to test for aldehydes and ketones

A

An orange-yellow ppt formed when 2,4-DNP reacts with aldehydes or ketones

25
Q

How can 2,4-DNP be used to identify specific aldehydes and ketones?

A

Add 2,4-DNP so that a ppt forms, purify the solid by recrystallisation, compare the melting point of the pure crystals formed with the melting points of 2,4-dinitrophenylhydrazones of all the common aldehydes and ketones

26
Q

What reagents can be used for the triiodomethane (iodoform) test?

A

Iodine and sodium hydroxide solution or potassium iodide and sodium chlorate (I) solutions

27
Q

Describe the method and results of the triiodomethane (iodoform) test

A

Iodine is added to a small amount of aldehyde/ketone followed by some sodium hydroxide to remove the iodine colour a very pale yellow ppt formed if aldehyde or ketone present

28
Q

What is the triiodomethane (iodoform) test used to identify?

A

The triiodomethane test (iodoform) is used to identify CH3CO- grps can be used to identify aldehydes and ketones

chem unit 4 (8 decks)

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