Nothing Special   »   [go: up one dir, main page]
Scribd Logo
Upload

Welcome to Scribd!

  • 24 views

    6 Carboxylic Acids

    Uploaded by

    Thinaya Jayarathne
    Carboxylic acids contain a carboxyl group (COOH) and have characteristic properties. They have higher boiling points than similar molecular weight compounds due to hydrogen bonding. Carboxylic acids can be prepared through oxidation of primary alcohols and aldehydes or hydrolysis of nitriles. Their reactions include reduction to primary alcohols, neutralization to form salts, halogenation to form acyl chlorides, and esterification with alcohols. Methanoic acid is an exception that can be oxidized to carbonic acid and carbon dioxide.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd

    6 Carboxylic Acids

    Uploaded by

    Thinaya Jayarathne
    24 views7 pages
    Carboxylic acids contain a carboxyl group (COOH) and have characteristic properties. They have higher boiling points than similar molecular weight compounds due to hydrogen bonding. Carboxylic acids can be prepared through oxidation of primary alcohols and aldehydes or hydrolysis of nitriles. Their reactions include reduction to primary alcohols, neutralization to form salts, halogenation to form acyl chlorides, and esterification with alcohols. Methanoic acid is an exception that can be oxidized to carbonic acid and carbon dioxide.

    Original Description:

    Original Title

    6 Carboxylic Acids (1)

    Copyright

    © © All Rights Reserved

    Available Formats

    PDF, TXT or read online from Scribd

    Did you find this document useful?

    Is this content inappropriate?

    Carboxylic acids contain a carboxyl group (COOH) and have characteristic properties. They have higher boiling points than similar molecular weight compounds due to hydrogen bonding. Carboxylic acids can be prepared through oxidation of primary alcohols and aldehydes or hydrolysis of nitriles. Their reactions include reduction to primary alcohols, neutralization to form salts, halogenation to form acyl chlorides, and esterification with alcohols. Methanoic acid is an exception that can be oxidized to carbonic acid and carbon dioxide.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    24 views7 pages

    6 Carboxylic Acids

    Uploaded by

    Thinaya Jayarathne
    Carboxylic acids contain a carboxyl group (COOH) and have characteristic properties. They have higher boiling points than similar molecular weight compounds due to hydrogen bonding. Carboxylic acids can be prepared through oxidation of primary alcohols and aldehydes or hydrolysis of nitriles. Their reactions include reduction to primary alcohols, neutralization to form salts, halogenation to form acyl chlorides, and esterification with alcohols. Methanoic acid is an exception that can be oxidized to carbonic acid and carbon dioxide.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 7

    IAL Chemistry Ms.

    Pabasari Goonetilleke
    Unit 4
    Organic Chemistry; carbonyls, carboxylic acids and chirality

    Carboxylic Acids

    • Carboxylic acids contains COOH group


    • They are only ………………………… in water which slightly dissociate, but they are strong enough to
    displace carbon dioxide from carbonates.

    • These have the ending …………………… but no number is necessary for the acid group as it must always
    be at the end of the chain
    • The numbering always starts from the carboxylic acid end
    • If there are carboxylic acid groups on both ends of the chain then it is called a - dioic acid

    pentanoic acid
    ………………………………………

    ………………………………………

    ………………………………………
    Bonding
    • Carboxylic acids contain the C=O bond and the single bonds in
    alcohol – Polar bonds
    • Many reactions of carboxylic acids involve loss of the hydrogen
    atom as H+ and form carboxylate ion (COO-)
    • The carboxylic acid salts are stabilised by delocalisation, which makes the dissociation more likely.
    • The delocalised ion has equal C-O bond lengths
    • If delocalisation did not occur, the C=O bond would
    be shorter than the C-O bond. The pi charge cloud has
    delocalised and spread out. The delocalisation makes the
    ion more stable and therefore more likely to form.

    Strength of carboxylic acids


    Physical Properties
    Carboxylic acids have distinctive smells and sour tases
    Examples:
    • Butanoic acid is responsible for the smell of stale sweat
    • Hexanoic acid for the smell of goats
    • Citric acid for sour taste of lemons

    Boiling Temperature

    • The presence of three polar bonds including a polar O-H


    …….…………………………………………………………………………………..
    gives rise to hydrogen bonds - so the boiling points are
    ………………………………………………………………………………………….
    higher compared with organic compounds with a similar molar mass
    ………………………………………………………………………………………….
    Londin forces between the non-polar hydrocarbon chain
    • …….…………………………………………………………………………………..
    length. Boiling temperature increases with the increasing of
    ……………………………………………………………………………………….
    molar mass
    ………………………………………………………………………………………….

    carbon chains increases so there is


    more London forces
    Hydrogen bonding shorter chain carboxylic acids give rise to dimers

    Solubility in Water
    • The smaller carboxylic (up to C4) acids dissolve in water in all proportions
    but after this the solubility rapidly reduces with increasing chain length.
    • They dissolve because they can hydrogen bond to the water molecules
    Methods of preparing carboxylic acids
    • Oxidation Reactions
    • Primary alcohols
    • Aldehydes carboxylic acids formation

    • Hydrolysis

    • CN bond breaks


    • C atoms remains as a part of the organic product
    • N atom becomes ammonia or ammonium ion

    Oxidation of Primary Alcohols

    Reaction: primary alcohol → carboxylic acid


    potassium dichromate(VI) solution and dilute sulphuric acid
    Reagent: ………………………………………………………………………………………………………………..
    Conditions: use an excess of dichromate, and heat under reflux: (distill off product after the reaction has
    finished)
    the orange dichromate ion (Cr2O72-) reduces to green Cr 3+ ion
    Observation: ………………………………………………………………………………………………………………..

    H-C-C-C-

    Oxidation of Aldehydes
    Reaction: aldehyde →carboxylic acid
    Potassium dichromate (VI) solution and dilute sulphuric acid
    Reagent: ………………………………………………………………………………………………………………..
    Conditions: heat under reflux
    Full Equation for oxidation
    1. Hydrolysis of Nitriles
    Reaction: Nitrile → carboxylic acid
    dilute hydrochloric acid/ sulphuric acid or aqueous alkali
    Reagent: ………………………………………………………………………………………………………………..
    Conditions: heat under reflux

    Acidic hydrolysis ………………………………………………………………………………………………………………..


    Alkaline hydrolysis ………………………………………………………………………………………………………………..
    The product is butanoate ion which is easily converted to butanoic acid by adding dilute acid
    ………………………………………………………………………………………………………………..

    The Reactions of Carboxylic Acids

    1. Reduction

    Reaction: carboxylic acid → primary alcohol


    LiAIH4 (Lithium tetrahydridoaluminate) in dry ether
    Reagents: ………………………………………………………………………………………………………………..
    Conditions: Room temperature and pressure
    Type of reaction: Reduction
    Role of reagent: Reducing agent
    Carboxylic acids cannot be reduced to aldehydes
    since any aldehyde formed will be immediately
    reduced to a primary alcohol
    2. Neutralization
    Carboxylic acids can be completely neutralized by reacting with aqueous alkali

    Carboxylate salts are ionic which are often shown with the formulae such as CH 3COO- Na+
    General formula: RCOONa

    Carboxylic acids can form salts with metals, alkalis and carbonates

    salit+hydrogen

    salt+water

    salt+water+CO2

    The effervescence caused by production of CO2 with carboxylic acids with solid Na2CO3 or aqueous
    NaHCO3 can be used as a functional group test for carboxylic acids

    3. Halagenation
    Reaction: carboxylic acid → acyl chloride
    Reagent: ……………………………………………………………..
    PCl5 phosphorous(V) chloride

    Conditions: room temp and anhydrous conditions (both reagent and acyl chloride react with water).
    Since the reaction is vigorous no heat is needed.
    This reaction with PCl5 (phosphorous(v)chloride) can be used as a test for carboxylic acids.
    misty fumes of HCL
    You would observe ……………………………………………… produced.
    hydrogen chloride

    POCl3 is a liquid that mixes with


    …………… + ………………. + ………….. the acyl chloride which should be
    therefore separated by fractional
    distillation HCl gas produced
    appear as misty fumes

    Ethanoyl Phosphorous
    chloride trichloride oxide
    4. Esterification
    Carboxylic acids react with alcohols, in the presence of a strong acid (often conc. sulfuric acid) catalyst,
    to form esters and water.

    Ester water

    Naming of ester includes two parts


    First – alkyl group from alcohol
    Second – carboxylate from carboxylic acid

    5. Oxidation of methanoic acid


    Carboxylic acids cannot be oxidised by using oxidising agents but methanoic acid is an exception as its
    structure has effectively an aldehyde group
    It forms carbonic acid (H2CO3) which can
    decompose to give CO2

    You might also like