carbonyls + carboxylic acids + esters Flashcards

1
Q

carbonyl definition

A

an organic moleucle that contains a C=O group

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2
Q

give 3 examples of carbonyl compounds

A

aldehydes, ketones, carboxylic acids

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3
Q

outline the test for carbonyl groups

A
  • react sample with 2,4-DNP, a pale orange solution
    POSITIVE= a condensation reaction will occur and a yellow-orange precipitate is formed
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4
Q

after a positive test result with 2,4-DNP, what can be done to identify the carbonyl compund

A

the melting point of the precipitate formed can be found, then this can be compared to a database to identify the carbonyl compound

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5
Q

outline a test for aldehydes

A
  • prepare a solution of 3cm3 AgNO3(aq) + 1 drop of NaOH to produce AgO a brown precipitate
  • add NH3 dropwise until precipitate redissolves- this is tollens reagent
  • add tollens reagent to the sample in a water bath at around 50C-60C
    POSITIVE= a silver mirror will form as the aldehyde is oxidised to a carboxylic acid as Ag+(aq) + e-&raquo_space; Ag(s)
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6
Q

why will ketones not react with tollens reagent

A

ketones cannot be oxidised, as there is no H group on the carbon with the C=O group to lose

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7
Q

by what mechanism do ketones normally react

A

nucleophilic addition

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8
Q

compare the reactivity of carbonyls and alkenes

A

carbonyls tend to be more reactive than alkenes, as the C=O bond is polar, due to the electronegativity difference between C and O, causing electron density to lie closer to the O, creating a dipole, so nucleophiles are attracted to the slight positive charge on the C atom
whereas C=C bonds are non polar

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9
Q

give the reagents and conditions to go from an aldehyde/ketone to an alcohol

A

reagent - NaBH4
conditions - aqueous
- just write it as [H] in equations, so you don’t have to worry about side products, but don’t forget to balance!

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10
Q

give the reagents and conditions to go from an aldehyde/ketone to a hydroxynitrile

A

reagents - NaCN + H2SO4 to form HCN in situ - HCN can be used in equations
conditions - aqueous

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11
Q

why is HCN alone not used as a reagent

A

HCN is a colourless + poisonous liquid, and is also very volatile as it boils slightly above room temp, so it cannot be safely used in a lab

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12
Q

give the reagents and conditions to go from an aldehyde to a carboxylic acid

A

reagents - K2Cr2O7
conditions - H2SO4 + heat under reflux
colour change from orange to green will occur

  • this reaction can also be used to identify an aldehyde
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13
Q

carboxylic acid definition

A

a compound with C=O carbonyl and OH hydroxyl functional groups bonded to the same carbon atom

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14
Q

why do carboxylic acids have high water solubility

A

C=O and O-H bonds are both polar, and these groups allow carboxylic acids to form hydrogen bonds with H2O

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15
Q

what structural factors affect the solubility of carboxylic acids

A

carbon chain length - as the length of the alkyl chain increases, solubility decreases as this is non polar

number of carboxyl groups - as number of carboxyl groups increases, solubility increases - dicarboxylic acids are very soluble

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16
Q

how do carboxylic acids act as acids

A

carboxylic acids are weak acids, as they only partially dissociate when dissolved in water, forming H+ and a carboxylate ion

carboxylic acids can undergo the same redox (with metals) and neutralisation (with bases) reactions as other acids - in both they will form carboxylate salts

17
Q

outline a test for carboxylic acids

A
  • react sample with Na2CO3
    POSITIVE= effervescence as gas is released, if this gas is bubbled through limewater it will turn limewater cloudy - this is because a neutralisation reaction occurs, carboxylic acids are the only common organic group acidic enough to react with carbonates
18
Q

what would be observed in a carboxylic acid was reacted with Na

A

effervescence and bubbling

19
Q

give the equation to produce an ester

A

alcohol + carboxylic acid <> ester + water
- this is a condensation reaction
- it is also a reversible reaction

20
Q

give the reagents and conditions to produce esters

A

reagents - alcohol + carboxylic acid
conditions - conc H2SO4 + reflux
- acid must be conc as too much water will cause the position of the equilibrium to shift and move to the reactants side, decreases yield of ester

21
Q

what are the 2 methods of hydrolysing esters

A

acid hydrolysis and alkali hydrolysis

22
Q

outline the process of acid hydrolysis of esters

A
  • ester is heated under reflux with dilute H2SO4 - it should be dilute as more water will move position of equilibrium to the reactant side, increasing break down of ester
  • products are alcohol and carboxylic acid
23
Q

outline the process of alkali hydrolysis

A
  • ester is heated under reflux with aqueous NaOH
  • products are carboxylate ion and alcohol
  • this is preferable, as it is not a reversible reaction so no ester will be reformed and therefore there will be a higher yield of products
24
Q

give the equation for producing acid anhydrides

A

2 carboxylic acid&raquo_space; acid anhydride

25
Q

outline how to name acid anhydride

A

replace acid with anhydride and if 2 acids are different, arrange names alphabetically
e.g. ethanoic anhydride
ethanoic propanoic anhydride

26
Q

give other methods of producing esters

A

reacting acid anhydrides/acyl chlorides/carboxylic acids with alcohols/phenols

27
Q

give the reagents and equation and conditions for the formation of acyl chlorides

A

reagents - thionyl chlorice (SOCl2)
carboxylic acid + SOCl2&raquo_space; acyl chloride + SO2 + HCl
- this reaction must take place in a fume hood, due to release of SO2 and HCl

28
Q

what reactions can acyl chlorides undergo

A

acyl chlorides are very reactive, and can easily be converted into carboxylic acid derivatives
e.g. esters

29
Q

give the reagents and conditions to go from an acyl chloride to a carboxylic acid

A

reagents - water
conditions - fume cupboard, this is a very vigorous reaction, and produces dense steam and HCl fumes
byproducts - HCl

30
Q

name the mechanism that acyl chlorides normally undergo

A

nucleophilic addition elimination

31
Q

give the reagents and by products to go from an acyl chloride to a primary amide

A

reagent - 2 ammonia + acyl chloride
byproducts - NH4Cl

32
Q

give the reagents and byproducts to go from a primary amide to a secondary amide

A

reagent - 2 primary amide + acyl chloride
byproducts - RNH3+Cl-
- the RNH3+ group comes from one of the primary amides

33
Q

compare the reactions of acyl chlorides and acid anhydrides

A

acid anhydrides react similarly to acyl chlorides with alcohols, phenols, water, ammonia - although they produce a carboxylic acid rather than HCl

however acid anhydrides are much less reactive than acyl chlorides

34
Q

what is another way than the production of esters can be more efficient/with higher yields

A

using acyl chlorides instead of carboxylic acids as the reaction is not reversible