Chemistry- Hydroxy compounds (alcohols)

what are the different types of alcohols and how do you classify them

primary, secondary and tertiary. Primary has an OH attached to a carbon with one other carbon attached, secondary has 2 carbons attached, tertiary has 3 carbons attached

what are the properties of alcohols

• colourless liquids at rtp

• boiling point increases with the number of C and OH groups

• boiling point decreases going from primary to tertiary

describe alcohol solubility

short chain alcohols are more soluble as they are able to form H bonds with water

• solubility decreases as C chain increases due to the molecule being made up of a more non polar section

what reactions can synthesise alcohols

1) alkene to alcohol through electrophilic addition

2) alkene to diol through oxidation

3) halogenoalkane to alcohol through nucleophilic substitution

4) aldehyde/ketone to alcohol through reduction

5) carboxylic acid to alcohol through reduction

6) ester to alcohol and carboxylic acid through hydrolysis

describe the reaction of alkene to alcohol and draw it out using the example of ethene

• reacts with steam

• uses H3PO4 as a catalyst as well as heat and pressure

• refer to cheat sheet for drawing

describe the general reaction of an alkene to diol, draw this reaction using ethene

reacting alkene with oxygen and water

• using the reagent of cold, diluted acidified potassium manganate

describe the reaction of halogenoalkane to alcohol

• is a nucleophilic substitution reaction that requires NaOH and heat

• OH is acting as nucleophile

describe the reaction of reduction of aldehydes and draw a general reaction for this

• reaction forms a primary alcohol

• NaBH4/LiAlH4 are reagents

• refer to cheat sheet for reaction

describe the reaction of the reduction of a ketone and draw out the general reaction

• forms a secondary alcohol

• NaBH4/LiAlH4 are reagents used

• refer to cheat sheet for reaction

describe the reaction of the reduction of a carboxylic acid, draw out general reaction

• primary alcohol formed

• LiAlH4 used

• refer to cheat sheet for general reaction

describe the hydrolysis of an ester and draw its general reaction

• formed when COOH reacted with strong acid

• catalyst of H2SO4/H3PO4 and heat under reflux

• the reverse reaction is hydrolysis of it as long as dilute acid used

• if strong alkali used in hydrolysis reaction, it becomes no longer reversible

• refer to cheat sheet for reaction

describe the acidity of alcohols, draw the dissociation of ethanol

• are very slightly acidic due to small degree of dissociation in water

• equilibrium lies very far to the left of the dissociation

• ethanol considered weaker acid than water

describe the combustion of alcohols, use combustion of ethanol

• complete combustion of alcohols: alcohol + oxygen —> carbon dioxide + water

• refer to cheat sheet for reaction

describe the substitution of alcohols

• is the same as the halogen reaction using the same reagents:

• HX, PCl3, PCl5, SOCl2

describe the reaction of alcohols with Na, write word and structure equation

• Na = reactive so easily breaks the OH bond

• gives off hydrogen gas as well as producing a basic compound

• a white crystalline solid of sodium alkoxide is formed when excess ethanol is evaporated off

• alcohol + sodium —> sodium alkoxide + hydrogen

• refer to cheat sheet for structural equation

how does the length of the hydrocarbon influence how vigorous the reaction is with Na

reaction becomes less vigorous with increasing hydrocarbon chain

describe the reaction of oxidation of alcohols

• primary alcohols can be oxidised: into aldehydes, further oxidised into COOH’s

• secondary alcohols can be oxidised: form ketones

• tertiary alcohols: can not be oxidised

• oxidising agents: acidified K2Cr2O7/KMnO4

why are the oxidising agents for these reagents in an acidified mixture

because they themselves need to be reduced, so the hydrogen ions needed for this are produced by the acid medium

what is observed when alcohols are oxidised by K2Cr2O7

the orange colour of the reagent is turned green

what is observed when the KMnO4 reagent is used when oxidising alcohols

purple to colourless

describe the oxidation of warm primary alcohol

• initially oxidised to aldehyde

• distillation of aldehyde can occur as this happens due to it having a lower bp

• if not distilled —> heat under reflux forms COOH

draw the reflux to convert alcohol to aldehyde

refer to cheat sheet

draw the oxidation of secondary alcohol using K2Cr207

refer to cheat sheet

describe the dehydration of alcohols, draw using ethanol

• undergo to form alkenes

• h2o is removed from larger molecule

• elimination reaction

• alcohol vapour passed over catalyst (Al2O3)

describe the esterification of alcohols, and draw the reaction using ethanol

• is the condensation between a COOH + alcohol to form an ester and a H2O molecule

• heated under reflux with strong acid of H2SO4

• carboxylic acid + alcohol —> ester + water

• is a reversible equilibrium

• refer to cheat sheet for reaction

what will happen testing for tertiary alcohol through oxidation

no change as they can not be oxidised

what other way can you use to distinguish alcohols

using the iodoform test

how is this other test for alcohols used

• identifies the presence of CH3CH2OH group, so ethanol or secondary alcohols —> others won’t give a positive result

• tri-iodomethane will form yellow ppt in presence of this group

draw tri-iodomethane

refer to cheat sheet