Alcohols 2/22/20 Alcohols Objective: To know about alcohols Outcomes: know that alcohols can be classified as primary, secondary or tertiary understand the reactions of alcohols with halogenating agents: - PCl5 to produce chloroalkanes - 50% concentrated sulfuric acid and potassium bromide to produce bromoalkanes - red phosphorus and iodine to produce iodoalkanes understand the reactions of alcohols with concentrated phosphoric acid to form alkenes by elimination In equations, the oxidising agent can be represented as [O].
Descriptions of the mechanisms of these reactions are not expected. Naming Alcohols The OH group is shown by removing the e from the ane of the name of the alkane and replacing with the suffix ol Just like ethanol. Draw: 1. 2. 3.
4. Methanol Propan-1-ol Propan-2-ol Propan-1,2-diol Draw and name: All the structural isomers of C4H11OH
What are alcohols? Alcohols are a homologous series of organic compounds with the general formula CnH2n+1OH and names ending ol. The functional group in alcohols is the hydroxyl group: OH. No. of carbon atoms 4 of 33 Molecular formula Name
1 CH3OH methanol 2 C2H5OH ethanol 3
C3H7OH propanol 4 C4H9OH butanol 5 C5H11OH
pentanol 6 C6H13OH hexanol Boardworks Ltd 2009 Naming alcohols Alcohols with three or more carbon atoms display positional isomerism. The number of the carbon to which the hydroxyl groups is attached is written before the ol.
propan-1-ol 5 of 33 propan-2-ol Boardworks Ltd 2009 Primary, secondary and tertiary What do you think this means? A chain of carbon atoms can be represented by R when drawing the structure. This is referred to as an R group.
Primary (1) alcohols have one R group attached to the carbon to which the OH group is attached. Secondary (2) alcohols have two R groups attached to the carbon to which the OH group is attached. Tertiary (3) alcohols have three R groups attached to the carbon to which the OH group is attached. 6 of 33
Boardworks Ltd 2009 Alcohols Objective: To know about alcohols Outcomes: know that alcohols can be classified as primary, secondary or tertiary understand the reactions of alcohols with halogenating agents: - PCl5 to produce chloroalkanes - 50% concentrated sulfuric acid and potassium bromide to produce bromoalkanes - red phosphorus and iodine to produce iodoalkanes understand the reactions of alcohols with concentrated phosphoric acid to form alkenes by elimination In equations, the oxidising agent can be represented as [O]. Descriptions of the mechanisms of these reactions are not expected.
Forming chloroalkanes from alcohols Primary, secondary and tertiary alcohols all react with phosphorus(V) chloride to form a chloroalkane. ROH + PCl5 RCl + HCl + POCl3 CH3CH2OH + PCl5 CH3CH2Cl + POCl3 + HCl Adding solid phosphorous(V) chloride to an alcohol at room temperature produces white HCl fumes, as well as the chloroalkane. This reaction can be used as a test for alcohols (the OH group), as well as a method of producing halogenoalkanes. 8 of 33 Boardworks Ltd 2009
You can also make chloroalkanes by reacting alcohols with hydrochloric acid. ROH + HCl RCl + H2O (CH3)3COH + HCl (CH3)3CCl + H2O This reaction is fastest with tertiary alcohols and slowest with primary alcohols Alcohols Objective: To know about alcohols Outcomes: know that alcohols can be classified as primary, secondary or tertiary understand the reactions of alcohols with halogenating agents: - PCl5 to produce chloroalkanes
- 50% concentrated sulfuric acid and potassium bromide to produce bromoalkanes - red phosphorus and iodine to produce iodoalkanes understand the reactions of alcohols with concentrated phosphoric acid to form alkenes by elimination In equations, the oxidising agent can be represented as [O]. Descriptions of the mechanisms of these reactions are not expected. Making bromoalkanes from alcohols Alcohols will react with compounds containing bromide ions (e.g. KBr) in a substitution reaction. The hydroxyl group (-OH) is replaced by the bromide, so the alcohol is transformed into a bromoalkane. The reaction uses an acid catalyst, e.g. 50% conc H2SO4
Making bromoalkanes from alcohols Example page 94 Alcohols Objective: To know about alcohols Outcomes: know that alcohols can be classified as primary, secondary or tertiary understand the reactions of alcohols with halogenating agents: - PCl5 to produce chloroalkanes - 50% concentrated sulfuric acid and potassium bromide to produce bromoalkanes - red phosphorus and iodine to produce iodoalkanes understand the reactions of alcohols with concentrated phosphoric acid to form alkenes by elimination In equations, the oxidising agent can be represented as [O].
Descriptions of the mechanisms of these reactions are not expected. Making iodoalkanes using red phosphorous and iodine If you react an alcohol with phosphorous triiodide (PI 3) you make an iodoalkane PI3 is usually made in situ (within the reaction mixture by refluxing the alcohol with red phosphorous and iodine 3ROH + PI3 3RI + H3PO3 Alcohols Objective: To know about alcohols Outcomes: know that alcohols can be classified as primary, secondary or tertiary
understand the reactions of alcohols with halogenating agents: - PCl5 to produce chloroalkanes - 50% concentrated sulfuric acid and potassium bromide to produce bromoalkanes - red phosphorus and iodine to produce iodoalkanes understand the reactions of alcohols with concentrated phosphoric acid to form alkenes by elimination In equations, the oxidising agent can be represented as [O]. Descriptions of the mechanisms of these reactions are not expected. Alcohols can be dehydrated to form alkenes You can make alkenes by eliminating water from alcohols in elimination reactions The alcohol is mixed with an acid catalyst such as con phosphoric acid (H3PO4)
The mixture is then heated The water is eliminated C2H5OH CH2 = CH2 + H2O The water molecule is made up from the hydroxyl group and a hydrogen atom that was bonded to a carbon atom adjacent to the hydroxyl group Alcohols can be dehydrated to form alkenes The water molecule is made up from the hydroxyl group and a hydrogen atom that was bonded to a carbon atom adjacent to the hydroxyl group This means that often there are two possible alkene products from one elimination reaction depending on which side of the hydroxyl group the hydrogen is eliminated from
Also the alkene products may be able to from E/Z isomers. If they can a mixture of both isomers will be made Alcohols can be dehydrated to form alkenes Example page 95 Alcohols Objective: To know about alcohols Outcomes: know that alcohols can be classified as primary, secondary or tertiary understand the reactions of alcohols with halogenating agents: - PCl5 to produce chloroalkanes - 50% concentrated sulfuric acid and potassium bromide to produce bromoalkanes - red phosphorus and iodine to produce iodoalkanes
understand the reactions of alcohols with concentrated phosphoric acid to form alkenes by elimination In equations, the oxidising agent can be represented as [O]. Descriptions of the mechanisms of these reactions are not expected. Alcohols Questions 1. Draw and name a primary alcohol, a secondary alcohol and a tertiary alcohol each with the formula C5H12O 2. Describe how ethanol could be converted into bromoethane 3. When 3-methyl-pentan-3-ol is heated with concentrated phosphoric acid it reacts to form a mixture of organic products a) What is the name of this type of reaction? b) How many organic compounds will be produced? A4
B3 C2 D 1 4. Iodoalkanes can be prepared from alcohols. a) State the two inorganic reagents needed to produce iodoalkanes from alcohols b) The mixture of reagents in part (a) produces phosphorous (III) iodide. Write an equation to represent the reaction between this and propan-1ol. Alcohols Questions 1. Draw and name a primary alcohol, a secondary alcohol and a tertiary alcohol each with the formula C5H12O 2. Describe how ethanol could be converted into bromoethane
E.g. React ethanol with sodium bromide (KBr) with a 50% concentrated sulfuric acid catalyst. Alcohols Questions 3. When 3-methyl-pentan-3-ol is heated with concentrated phosphoric acid it reacts to form a mixture of organic products a) What is the name of this type of reaction? Elimination reaction or dehydration reaction b) How many organic compounds will be produced? A4 B3 C2 D 1
Alcohols Questions 4. Iodoalkanes can be prepared from alcohols. a) State the two inorganic reagents needed to produce iodoalkanes from alcohols Red phosphorus and iodine b) The mixture of reagents in part (a) produces phosphorous (III) iodide. Write an equation to represent the reaction between this and propan-1-ol. 3CH3CH2CH2OH + PI3 3CH3CH2CH2I + H3PO3 Alcohols Objective: To know about alcohols Outcomes: know that alcohols can be classified as primary, secondary or tertiary
understand the reactions of alcohols with halogenating agents: - PCl5 to produce chloroalkanes - 50% concentrated sulfuric acid and potassium bromide to produce bromoalkanes - red phosphorus and iodine to produce iodoalkanes understand the reactions of alcohols with concentrated phosphoric acid to form alkenes by elimination In equations, the oxidising agent can be represented as [O]. Descriptions of the mechanisms of these reactions are not expected.
