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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
What are the Methods to convert carboxylic acids (COOH) to esters (COOR)?
1. Fisher Esterification using alcohols 2. Conversion to acid chlorides and then reaction with alcohols to give esters
26
In the 2nd step of conversion of COOH to ester, what does the pyridine do
neutralise the HCl generated Otherwise, alcohols (especially tertiary alcohols) may dehydrate under strongly acidic conditions
27
What are the Methods to convert carboxylic acids (COOH) to amides (CONH2)?
1. Condensation of Acids with Amines: Direct Synthesis of Amides 2. Conversion to acid chlorides and then reaction with ammonia or amines
28
What are the role of Pyridine or NaOH in the second step of conversion of COOH to amine?
prevent HCl from protonating the amine
29
formula of acid chloride
COCl
30
Synthesis and use of Acid Chlorides (COCl) good/ bad for nucleophilic sub?
Halide ions: excellent leaving groups for nucleophilic acyl substitution
31
What is acid chlorides activated by?
COOH
32
Carbonyl O and Cl make the acyl C atom
strongly electrophilic
33
2 steps of Synthesis and use of Acid Chlorides (COCl):
1. Addition–elimination mechanism of nucleophilic acyl substitution 2. Thionyl chloride (SOCl2) or Oxalyl chloride [ (COCl2) ] form gaseous by-products
34
Synthesis and use of Acid Chlorides (COCl) 4 reactions with different compounds = what are the products?
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
Aldehyde or COOH more reactive toward most reducing agents?
Aldehyde
36
Lithium tri-tert-butoxyaluminum hydride _______ acid chlorides to aldehydes
reduces
37
ester is a combination of
COOH and alcohol with loss of H2O (COOH acid derivative) hydroxyl group (-OH) is replaced by a alkoxy group (OR-)
38
Reaction mechanism between RCOOH and RCOCl to RCOCOR (anhydride)
nucloephile > good leaving group > deprotonation > acyl group > very reactive - useful synthetic intermediates
39
Define Carboxylic acid derivatives:
Compounds with functional groups that can be converted to carboxylic acids by a simple acidic or basic hydrolysis
40
What are the most important carbon derivatives?
ester amide nitriles
41
Compounds with functional groups that can be converted to carboxylic acids by a simple acidic or basic __________
hydrolysis
42
Composite of a carboxylic acid and ammonia or an amine
acid + amine > ammonium carboxylate salt > amide (drive off water and force reaction to completion)
43
primary, secondary and tertiary amide:
one R group 2 R groups 3 or more R groups
44
what bonds does nitriles have? (CN)
triple
45
Lack the C=O but classified as acid derivatives
hydrolyse to give carboxylic acids
46
what is the bond angle of R CN (nitrile, triple bond)
180, sp hybridised
47
Halide ions: good/ bad leaving groups fro nuc sub?
excellent leaving groups for nucleophilic acyl substitution
48
Addition–elimination mechanism of nucleophilic acyl substitution
Acid chlorides (acyl chlorides): activated form of a carboxylic acid Carbonyl O and Cl make the acyl C atom strongly electrophilic
49
Acid Anhydrides (RCOCOR)
Contain two molecules of an acid with loss of H2O Activated form of a carboxylic acid. Carboxylate group leaves
50
Nucleophilic Acyl Substitution
one nucleophile replaces another on the acyl (C=O) carbon atom. Addition-Elimination
51
Interconversion of Acid derivatives; 3 steps
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
Favourable reactions convert a more reactive acid derivative to a less reactive one
Basicity of the leaving group (Strong bases not good leaving groups)
53
Diagram of interconversion of acid derivatives
slide 26 lec COOH
54
Interconversion of Acid derivatives 1) acid chloride
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
Interconversion of Acid derivatives 2. Acid Anhydrides
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
Interconversion of Acid derivatives 3. Esters
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
All acid derivatives hydrolyse to give carboxylic acids
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
Saponification:
“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
What agent to reduce COOH derivatives
LiAlH4
60
Reduction of COOH acid derivatives 1. Alcohols
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
Reduction of Carboxylic Acid Derivatives 2. Aldehydes
Lithium tri-tert-butoxyaluminum hydride: mild reducing agent ( for acid chloride) Diisobutylaluminum hydride (DIBAL-H): stronger reducing agent ( for ester / nitrile )
62
Reduction of Carboxylic Acid Derivatives 3. Amines
Lithium aluminium hydride reduces amides and nitriles to amines sec amides > sec amiNes tet" > tet" prim">prim"
63
Reactions with Organometallic Reagents 1. Esters and Acid Chlorides
Grignard and organolithium reagents add twice to acid chlorides and esters add H3O+ unstable intermediate > ketone > akloxide > 3 alcohol (tet)
64
Summary of the chemistry of Acid Chlorides
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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