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PMP-102 > Carboxylic acids and derivatives > Flashcards

Carboxylic acids and derivatives Flashcards

1
Q

Carboxyl group

A

combination of a C=O and a -OH on the same C

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2
Q

Aliphatic acid

A

alkyl group bonded to the carboxyl group

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3
Q

Aromatic acid

A

aryl group bonded to the carboxyl group

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4
Q

Weak acids compared with the mineral acids,
but they are ____ acidic than alcohols or phenols

A

more

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5
Q

resonance-stabilisation of the carboxylate anion RCO2-

A

resonance stabilised > p-orbital overlap

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6
Q

sp2 hybrid carbonyl C atom is planar, with nearly trigonal bond angles

how is the group polar?

A

the difference in electronegativity between C=O pushes the e- towards the oxygen - very polar

dipole-dipole

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7
Q

How many lone pairs does oxygen have in carboxylic acids?

A

2O

= lone pairs in total

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8
Q

Carboxylic dimer:

A

two monomers of carboxylic

hydrogen bonds H from one monomer attaches from O of other k=monomer (using the lone pairs - covalent)

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9
Q

water with carboxylic groups

A

H-bonds with H2O

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10
Q

How is a salt of a carboxylic acid formed?

A

carboxylic acid with M+ OH-

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11
Q

Synthesis of Carboxylic acids (RECAP)
3 steps

A
  1. Oxidation of primary alcohols and aldehydes
  2. Oxidative cleavage of alkenes and alkynes
  3. Carboxylation of Grignard reagents [alkyl aryl halide]
  4. Formation and hydrolysis of nitriles [SN2 reaction]
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12
Q

Reactions Carboxylic acids - 4 major types of reactions

A

1) deportation
2) nucleophilic acyl substitution
3) reduction
4) decarboxylation

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13
Q

Carboxylate anion ; nucleophile/ electrophile?

A

weak base - can act as a nucleophile

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14
Q

oxidation of primary alcohol >

A

aldehyde (NaOCL/ H2CrO4) > carboxylic acid (same)

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15
Q

oxidative cleavage - glycol >

A

ketone > aldehyde > carboxylic acid

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16
Q

acetate ion and benzyl bromide >

A

benzyl acetate (SN2 mechanism) = ESTER

(the Br is the leaving grousp - e- moved to it to make a bromide anion

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17
Q

Nucleophilic Acyl Substitution:
(most common method for interconverting carboxylic and derivatives)

A

one nucleophile replaces another on
the acyl (C=O) carbon atom

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18
Q

Nucleophilic Acyl Substitution Basic conditions: Hydrolysis of an Ester
2 parts

A

Step 1: Hydroxide ion (strong nucleophile) adds to C=O, forming tetrahedral intermediate

Step 2: An alkoxide ion leaves, regenerating the C =O double bond and stabilises itself

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19
Q

ester + OH

A

basic hydrolysis of ester is an example of nucleophilic substitution (basic)

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20
Q

acid + alkoxide
>

A

carboxylate + alcohol

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21
Q

Nucleophilic Acyl Substitution Acid conditions: Fisher Esterification

A

Part 1: Acid-catalysed addition of the alcohol to the carbonyl group

Part 2: Acid-catalysed dehydration

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22
Q

what is the fisher esterification?
Equilibrium

A

Protonation of the carbonyl

nucleophilic attack on the carbonyl

the proton transfer to the OH group

the removal of water

the deprotonation step

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23
Q

Fisher esterification
part 1: Acid-catalysed addition of the alcohol to the carbonyl group

A

Protonation activates C=O

Alcohol addition
(weak nucleophile)

Deprotonation completes the reaction

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24
Q

Fisher esterification
Part 2: Acid- catalysed dehydration

A

Protonation prepares the OH group to leave

Water leaves

Deprotonation completes the reaction (gives an ester)

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25
Q

What are the Methods to convert carboxylic acids (COOH) to esters (COOR)?

A
  1. Fisher Esterification using alcohols
  2. Conversion to acid chlorides and then reaction with alcohols to give esters
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26
Q

In the 2nd step of conversion of COOH to ester, what does the pyridine do

A

neutralise the HCl generated

Otherwise,
alcohols (especially tertiary alcohols) may dehydrate under strongly acidic conditions

27
Q

What are the Methods to convert carboxylic acids (COOH) to amides (CONH2)?

A
  1. Condensation of Acids with Amines: Direct Synthesis of Amides
  2. Conversion to acid chlorides and then reaction with ammonia or amines
28
Q

What are the role of Pyridine or NaOH in the second step of conversion of COOH to amine?

A

prevent HCl from protonating the amine

29
Q

formula of acid chloride

A

COCl

30
Q

Synthesis and use of Acid Chlorides (COCl)
good/ bad for nucleophilic sub?

A

Halide ions: excellent leaving groups for nucleophilic acyl substitution

31
Q

What is acid chlorides activated by?

A

COOH

32
Q

Carbonyl O and Cl make the acyl C atom

A

strongly electrophilic

33
Q

2 steps of Synthesis and use of Acid Chlorides (COCl):

A
  1. Addition–elimination mechanism of nucleophilic acyl substitution
  2. Thionyl chloride (SOCl2) or Oxalyl chloride [ (COCl2) ] form gaseous by-products
34
Q

Synthesis and use of Acid Chlorides (COCl)
4 reactions with different compounds = what are the products?

A
  1. Reaction with alcohols to form esters (RCOR1)
  2. Reaction with ammonia or amines to form amides (RCONHR1)
  3. Reaction with carboxylic acids to form anhydrides (RCOCOR)
  4. Reduction to aldehydes
35
Q

Aldehyde or COOH more reactive toward most reducing agents?

A

Aldehyde

36
Q

Lithium tri-tert-butoxyaluminum hydride _______ acid chlorides to aldehydes

A

reduces

37
Q

ester is a combination of

A

COOH and alcohol with loss of H2O
(COOH acid derivative)
hydroxyl group (-OH) is replaced by a alkoxy group (OR-)

38
Q

Reaction mechanism between RCOOH and RCOCl to RCOCOR (anhydride)

A

nucloephile > good leaving group > deprotonation > acyl group > very reactive - useful synthetic intermediates

39
Q

Define Carboxylic acid derivatives:

A

Compounds with functional groups that can be converted to carboxylic acids by a simple acidic or basic hydrolysis

40
Q

What are the most important carbon derivatives?

A

ester
amide
nitriles

41
Q

Compounds with functional groups that can be converted to carboxylic acids by a simple acidic or basic __________

A

hydrolysis

42
Q

Composite of a carboxylic acid and ammonia or an amine

A

acid + amine > ammonium carboxylate salt > amide (drive off water and force reaction to completion)

43
Q

primary, secondary and tertiary amide:

A

one R group
2 R groups
3 or more R groups

44
Q

what bonds does nitriles have? (CN)

A

triple

45
Q

Lack the C=O but classified as acid derivatives

A

hydrolyse to give carboxylic acids

46
Q

what is the bond angle of R CN (nitrile, triple bond)

A

180, sp hybridised

47
Q

Halide ions: good/ bad leaving groups fro nuc sub?

A

excellent leaving groups for nucleophilic acyl substitution

48
Q

Addition–elimination mechanism of nucleophilic acyl substitution

A

Acid chlorides (acyl chlorides): activated form of a carboxylic acid

Carbonyl O and Cl make the acyl C atom strongly electrophilic

49
Q

Acid Anhydrides (RCOCOR)

A

Contain two molecules of an acid with loss of H2O

Activated form of a carboxylic acid. Carboxylate group leaves

50
Q

Nucleophilic Acyl Substitution

A

one nucleophile replaces another on the acyl (C=O) carbon atom. Addition-Elimination

51
Q

Interconversion of Acid derivatives; 3 steps

A

Step 1: Addition of the nucleophile gives a tetrahedral intermediate

Step 2: Elimination of the leaving group regenerates the carbonyl group

Acyl transfer reactions (RCO)

52
Q

Favourable reactions convert a more reactive acid derivative to a less reactive one

A

Basicity of the leaving group
(Strong bases not good leaving groups)

53
Q

Diagram of interconversion of acid derivatives

A

slide 26 lec COOH

54
Q

Interconversion of Acid derivatives
1) acid chloride

A

COOH > anhydride

aklcohol > ester (pyridine (or another base) added to the solution to neutralise the HCl by-product)

amine > amide (Reaction with ammonia gives a primary amide. With a primary amine gives a secondary amide; and with a secondary amine, it gives a tertiary amide)

55
Q

Interconversion of Acid derivatives
2. Acid Anhydrides

A

alcohol > ester
amine > amide [Reaction with ammonia gives a primary amide. With a primary amine gives a secondary amide; and with a secondary amine, it gives a tertiary amide]

56
Q

Interconversion of Acid derivatives
3. Esters

A

amine > amide [Heating with ammonia or an amine (Ammonolysis) ]

Acyl group: transferred from O of the alcohol to the N atom of the amine

Reaction with ammonia gives a primary amide. With a primary amine gives a secondary amide; and with a secondary amine, it gives a tertiary amide

57
Q

All acid derivatives hydrolyse to give carboxylic acids

A
  1. Acid Halides and Anhydrides: Easily hydrolyse under neutral conditions
  2. Esters (Acid-catalysed: reverse of Fischer esterification equilibrium)
  3. Amides (hydrolise - basic/acid conditions) [Strong conditions: prolonged heating in 6 M HCl or 40% aqueous NaOH ]
  4. Nitriles - Stronger conditions
    hydrolyse to the carboxylic acid
58
Q

Saponification:

A

“the making of soap.” Soap is made by the basic hydrolysis of fats, which are esters of long-chain carboxylic acids with the triol glycerol

59
Q

What agent to reduce COOH derivatives

A

LiAlH4

60
Q

Reduction of COOH acid derivatives
1. Alcohols

A

LiAlH4 reduces acids, acid chlorides, anhydrides, and esters to primary alcohols
reduces carboxylic acids, esters and acid chlorides to primary alcohols going through aldehyde, but it cannot be isolated

61
Q

Reduction of Carboxylic Acid Derivatives
2. Aldehydes

A

Lithium tri-tert-butoxyaluminum hydride: mild reducing agent ( for acid chloride)

Diisobutylaluminum hydride (DIBAL-H): stronger reducing agent ( for ester / nitrile )

62
Q

Reduction of Carboxylic Acid Derivatives
3. Amines

A

Lithium aluminium hydride reduces amides and nitriles to amines
sec amides > sec amiNes
tet” > tet”
prim”>prim”

63
Q

Reactions with Organometallic Reagents
1. Esters and Acid Chlorides

A

Grignard and organolithium reagents add twice to acid chlorides and esters

add H3O+

unstable intermediate > ketone > akloxide > 3 alcohol (tet)

64
Q

Summary of the chemistry of Acid Chlorides

A

a) Synthesis of Acid Chlorides

b) Reactions of Acid Chlorides

c) Synthesis of Acid Anhydride

d) Reactions of Acid Anhydrides

e) Synthesis of Esters

f) Reactions of Acid Anhydrides

g) Synthesis of Amides

h) Reactions of Amides

i) Synthesis of nitriles

j) Reactions of Nitriles

PMP-102 (49 decks)

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