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Chemistry #2 > carboxyllic acids > Flashcards

carboxyllic acids Flashcards

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1
Q

what’s a property of carboxylic acids with very low molecular mass

why?

A

they are very soluble in water

because the -COOH forms hydrogen bonding with water

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2
Q

do carboxyllic acids slightly or strongly dissociate in water

so are they strong or weak

A

slightly

weak

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3
Q

what is formed when carboxyllic acids slightly disassociate

A

carboxylate ion and hydrogen ion

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4
Q

how do carboxylic acids dissociate

A

the carbonyl group attracts electrons away from the -OH bond, which leads to the -OH bond being weakened therefore it breaks more easily to form a carboxylate ion and hydrogen ion

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5
Q

why are alcohols not acidic even if they have OH bond

A

bc the bond in alcohols doesn’t break easily

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6
Q

how does the addition of a halogen onto carboxylic acids changes its acidity

A

it makes it more acidic

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7
Q

why does the addition of a halogen onto carboxylic acids increase its acidity

A

the halogen atom is more electronegative and so withdraws electron density away from the carbonyl carbon.

this causes the OH bond to become more polar which results in the OH bond weakening .

the H in the OH bond is lost more easily lost so chloroethanoic acid is more acidic than ethanoic acid

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8
Q

how do we test for carboxyllic acids

A

reacting with sodium carbonate Na2CO3

effervescence is observed from CO2

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9
Q

eg what is formed when sodium ethanoic acid reacts sodium carbonate

A

co2 + water + sodium ethanoate

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10
Q

what’s formed when carboxylic acids react with alcohol in the presence of concentrated sulphuric acid

what’s the reaction called

A

ester and water

esterifcation

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11
Q

what are 3 uses of esters

A

flavourings , perfume , plasticisers

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12
Q

how do we name esters

A

alcohol bit then carboxylic acids bit

eg

methyl ethanoate

(methanol+ethanoic acid)

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13
Q

how many ways to make esters

A

3

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14
Q

are carboxyllic acids and esters isomers of one another

A

yes, functional group isomers

same molecular formula different structural formula

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15
Q

what are 2 ways the hydrolyse esters

A

acid hydrolysis

basic hydrolysis

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16
Q

how are esters hydrolysed using acid hydrolysis

A

this is a reversible reaction.

esters can be hydrolysed using water and dilute H2SO4/HCl to form the alcohol and carboxylic acid

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17
Q

how do we make hydrolysis complete as possible in acid hydrolysis of ester because it’s a reversible reaction

A

excess of water

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18
Q

as acid hydrolysis of ester is a reversible reaction, this gives a low yield of carboxylic acid and alcohols , therefore there an alternative 2 step method

what is the method

A

basic hydrolysis

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19
Q

what happens in the first step of basic hydrolysis of ester

A

when an ester is heated with alcohol , it is hydrolysed into an alcohol and carboxylate salt

20
Q

what happens in the 2nd step of basic hydrolysis of ester

A

we add an excess of dilute HCl or dilute H2SO4 to the carboxylate salt to reform the carboxylic acid

21
Q

how do we make soaps from fats

A

triglycerides can be hydrolysed using HOT NaOH or KOH to form glycerol (a useful solvent) and sodium or potassium carboxylate salts (these are used to manufacture soaps)

22
Q

whys glycerol a good solvent

A

it has 3 OH bonds therefore forms hydrogen bonds easily in water

23
Q

definition of biodiesel

A

liquid fuel consisting of a mixture of methyl esters of long chain carboxylic acids from vegetable oils

24
Q

how do we make biodiesel

A

the oil is reacted with methanol with a strong acid / alkali catalyst to form a mixture of methyl esters which can be used a fuel in diesel vehicles

the products are mixtures of methyl esters and glycerol

25
Q

carboxylic acids can be turned into other functional groups to be used in organic synthesis.

so what 2 groups can be formed from carboxylic acids

A

acyl chlorides

acid anhydrides

26
Q

how are acyl chlorides formed

A

the -OH group on the carboxylic acid is replaced with a chlorine atom

27
Q

how are acyl chlorides named

A

CH3COCl is derived from ethanoic acid
and therefore it is called ethanoyl chloride

28
Q

the carboxylic acid derivative (acyl chloride) possesses a good leaving group (Cl) which also…

A

withdraws electrons from the carbonyl carbon making the carbon more reactive

29
Q

what’s a good leaving group

A

a stable species which is removed during a chemical reaction

30
Q

what reaction do acyl chlorides and acid anhydrous react with nucleophiles

A

nucleophillic addition elimination

and reduction reaction

31
Q

what do the reactions of acyl chlorides and acid anhydrous involve

A

it involves the replacement of the leaving group eg Cl- by the nucleophile

32
Q

what’s formed when acyl chlorides react with water

A

carboxylic acids

33
Q

what’s formed when acyl chlorides react with alcohol

A

esters

34
Q

what’s formed when acyl chlorides react with ammonia

A

amides

35
Q

what’s formed when acyl chlorides react with amines

A

substituted amides

36
Q

why are acyl chlorides more preferred in the formation of esters than carboxyllic acids

A

1) no need for acid catalyst (H2SO4)

2) purer product

3) more yield as reaction isn’t reversible

37
Q

why’s the other carboxylic acid derivative acid anhydrides preferred over acyl chlorides in the formation of esters

A

1) no corrosive HCl formed

2) acid anhydrides less vulnerable to hydrolysis

38
Q

what’s the -OH group replaced with in carboxylic acids to make acid anhydrides

A

-OCOR

39
Q

how are acid anhydrides formed

A

acid anhydrides are formed when 2 molecules of carboxylic acids join together with the elimination of water

40
Q

how do we name acid anhydrides

A

The acid anhydride is named after the carboxylic acid that was used in its synthesis.

then we just add anhydride to the end

eg : ethanoic anhydride

or ethanoic propanoic anhydride

41
Q

do acid anhydrides have a good leaving group and why

what happens when the good leaving group leaves

A

yes acid anhydrides good leaving group is - âž–OCOR

because a leaving group is a stable species that is removed during a chemical reaction

when the good leaving group leaves it activates the adjacent carbonyl group by electron withdrawal

42
Q

acid anhydrides react with the same nucleophiles as acyl chlorides to form the same products which are…

A

water to form carboxylic acids

alcohols to form esters

ammonia to form amides

amines to form substituted amides

43
Q

acyl chlorides and acid anhydrides react in the same way as their corresponding
carboxylic acid but ….

A

will produce a different side product

eg acid anhydrides and alcohol = ester and carboxylic acids

eg acyl chloride and alcohol= ester and HCl

eg carboxylic acid and alcohol = ester and H2O

44
Q

what do acid anhydrides react with to form carboxyllic acids

A

water

(nucleophillic addition elimination mechanism too)

45
Q

what are the 3 ways to make carboxylic acids

A

1) primary alcohols / aldehydes oxidised by acidified potassium dichromate to form carboxylic acids and water

2) acyl chlorides and water to form carboxyllic acids and HCl

3) acid anhydrides and water to form 2 molecules of carboxylic acids

46
Q

how do acid anhydrides react with to form esters

A

with alcohol

47
Q

what are 3 ways to make esters

A

1) carboxylic acid and alcohol (esterifcation)

2) acyl chloride and alcohol

3) acid anhydrides and alcohol

Chemistry #2 (10 decks)

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