Carbonyl compounds Flashcards
Ketone
- COC-
eg. ButanONE
Aldehyde
-CHO
eg butenAL
Alkyl
Alkane with H atom removed
Aryl
Cyclic compound containing benzene ring
Why is carbonyl group polar?
C=O bond polar due to electronegativity on oxygen atom - more electrons in bond (Pi and sigma) towards O atom
Why is C=O soluble in water?
Polar so smaller aldehydes and ketones are soluble in water - form H bonds (up to 4 carbons in the chain)
Why do ketones and aldehydes has higher boiling points than alkanes?
Permanent dipole-dipole forces between molecules
What is the oxidising agent used in the oxidation of alcohols and aldehydes?
[O] = Potassium dichromate (VI) with sulfuric acid or acidified potassium dichromate (Cr3O72-) which is orange and goes to green Cr3+
Conditions for primary alcohol ➡️ Aldehyde and ?
Heat gently and distill using oxidising agent
Forms 1 molecule of water too
Conditions for oxidisation of ketone to carboxylic acid and ?
Heat under reflux with excess H2SO4 and oxidising agent
1 molecule of water also forms
Cannot be oxidising further
Condistions for secondary alcohol ➡️ ketone
Heat gently using oxidising agent
Forms 1 molecule of water too
Cannot be oxidised further and tertiary alcohols cannot be oxidised at all
Reducing agent for reduction of carbonyl compounds
2[R] = ️sodium tetrahydridborate (III), NaBH4, which is a source of H-
Conditions for reduction of aldehydes ➡️ primary alcohols and ketones ➡️ secondary alcohols
Warm using reducing agent and water as the solvent
Mechanism for reduction of carbonyl compounds
Nucleophilic addition
1) nucleophilic attack H- with lone pair to Cdelta+ and pair of electrons from Pi bond to Odelta-
2) adding water - lone pair on O- goes to H atom on water and pair of electrons in H-O bond goes to the O
Forms an alcohol and OH- molecule
Brady’s reagent test
2,4-dinitrophenylhydrazine
Addiction across a double bond and elimination of water means ghat a C=O bond is present
Forms a yellow/orange precipitate with only aldehydes and ketones
To find specific ketone or aldehyde, the mpt of the crystals formed can be compared with a database
Silver mirror test
Tollens’ reagent - ammonical silver nitrate [Ag(NH3)2]+
Add tollens’ reagent and warm gently in a water bath
A silver mirror forms on the side of the test tube from a colourless solution with aldehydes only
The aldehyde is oxidised and Ag+ reduced
No silver mirror with ketones as cannot be oxidised further
Carboxylic acids
-COOH
Why do carboxylic acids partially dissociate?
Weak acids
Why are carboxylic acids soluble in water?
Highly polar - C=O and O-H
Form H bonds - 2 per molecule
Only soluble up to 4 C in chain length as longer chain non-polar
Carboxylic acid + metal ➡️
Metal salt + H2
Carboxylic acid + carbonate
Metal salt + CO2 + H2O
Carboxylic acid + base ➡️
metal salt + water
Esters
-COOC
From carboxylic acid and alcohol
Name alcohol then acid eg ethyl propanoate
Formation with carboxylic acid and alcohol
With conc H2SO4 catalyst
Goes to ester and water
Formation from acid anhydride and alcohol
Acid anhydride - 2 carboxylic acids with water molecule removed
React with alcohol - forms ester (usual naming - alcohol then acid) and a carboxylic acid
Forms a better yield of ester as not reversible
Uses of esters
Perfumes
Food flavourings
Oils
Acid hydrolysis of esters
Reflux ester with dilute H2SO4 or HCl
Ester + water (reversible) ➡️ carboxylic acid and alcohol
Alkali hydrolysis of esters
Reflux with alkali eg NaOH
Ester + NaOH ➡️ metal salt + alcohol
What is a triglyceride?
- a triester of propane-1,2,3-triol (glycerol) and a fatty acid (octadecanoic or hexadecanoic acid). All 3 alcohol groups esterified
What does C18,1(9) mean?
18 carbons, 1 double bond on the 9th carbon of a fatty acid (carboxylic acid)
There are trans and cis versions of this
Why are saturated and trans fatty acids worse for health?
Pack together more closely a solid and block arteries leading to CHD and increased heart attack risk
Contain bad LDL cholesterol which sticks to artery walls and plaque builds up
Why are monounsaturated and polyunsaturated fatty acids better for health?
Contain good HLD (high lipo-density) cholesterol which carries bad cholesterol away from arteries so lower blood pressure and lower risk of CHD
What is biodiesel made from?
Vegetable oil or animal fat - long chain alkyl esters
Triglyceride + 3H3OH (reversible + NaOH) ➡️ 3H3C-O-C=O + glycerol
What is biodiesel used in and what are the issues?
Used in standard Diesel engines or blended with petrodiesel
Carbon neutral: same amount of CO2 absorbed when growing as is released when burned as a fuel
But may lead to increase in food prices and starvation
