UNIVERSITI TUNKU ABDUL RAHMAN

FACULTY OF SCIENCE

BACHELOR OF SCIENCE (HONS) BIOCHEMISTRY

YEAR 1 TRIMESTER 3

UDEC 1164 ORGANIC CHEMISTRY

Name Sri Sangliswaran s/o Subramaniam

ID 1203776

Experiment Title Experiment 4: Properties of Alcohols

Partners Nurul Maswin bt Anaqi SuenTan Chai YuinBeh Wan Chin

Date of Submission 25.2.2015 (week7)

Title: Properties of Alcohols

Objectives : To study the properties of alcohol

To determine the reactivity of alcohol

To determine the nature of given alcohols by using several chemical tests.

Introduction :

Simple hydrocarbon chains or rings that contain a hydroxyl group (-OH) bonded to a

carbon atom are called alcohols. The following are several such compounds:

An alcohol is any organic compound in which the hydroxyl functional group (-O H) is bound to a hydrocarbon chain. The suffix -ol appears in the IUPAC chemical name of all substances where the hydroxyl group is the functional group with the highest priority; in substances where a higher priority group is present the prefix hydroxy- will appear. The general formula for alcohol is CnH2n+1OH.

As shown above if the carbon atom is bonded to three hydrogen atoms in addition to the –OH, the alcohol is methanol. If the carbon bonded to the –OH is bonded to one alkyl group and two hydrogen atom, the alcohol is primary alcohol (1o). If the carbon that is bonded to the –OH is bonded to two alkyl group and one hydrogen atom, the alcohol is a secondary (2 o) alcohol. If the carbon that is bonded to the –OH is bonded to three alkyl group, the alcohol is a tertiary (3o) alcohol. All of these alcohols share some characteristics but other characteristics are different owing to their different structures.

Physical Properties

The larger an alcohol the higher the boiling point, usually. Small alcohols are water soluble because the hydroxyl groups can hydrogen bond with water molecules. But as the size of the alkyl group increases the solubility in water decreases. This is the result of the alkyl group disrupting hydrogen bonding among the water molecules. If the disruption becomes large enough the water molecules, in effect, expel the alcohol molecules to reestablish hydrogen bonding.

Chemical Properties

Methanol Ethanol propan-2-ol 2-methylpropan-2-ol

The chemical test taken into consideration are those that assist in the identification of the classes of alcohols.

1. Lucas Test

This test is used to distinguish among primary, secondary and tertiary water-soluble alcohols. Lucas reagent is a mixture of concentrated hydrochloric acid and zinc nchloride. Zinc chloride is a Lewis acid, which when added to hydrochloric acid makes it even more acidic. Water soluble tertiary alcohols react with Lucas reagent almost immediately to form an alkyl chloride which is insoluble in the aqueous solution. The formation of a second liquid phase in the test tube almost as soon as the alcohol initially dissolves is indicative of a tertiary alcohol. A secondary alcohol reacts slowly to form a chloride and, after heating a little, gives a second phase, usually within ten minutes. Primary alcohols and methanol do not react under these conditions.

2. Chromic Acid Test

Primary alcohols are oxidized to carboxylic acids by chromic acid. The Cr+6 ions in the chromic acid, which is red-brown, is reduced to Cr+3 ions, which is green. Secondary alcohols are oxidized to ketones by chromic acid. The chromium reduction is the same here as for the primary alcohols. Tertiary alcohols are not oxidized by chromic acid. Thus, this reaction can distinguish between primary and secondary alcohols, on the one hand, and tertiary alcohols, on the other.

3. Reaction with Metallic Sodium

Alcohols, like water, are weak acids. The hydroxyl group can act as a proton donor to form an alkoxide ion. Alkoxide ions dissolved in alcohol, like hydroxide ions in water, are strong bases which can be prepared by the reaction of an alcohol with sodium metal. This reaction produces hydrogen gas.

2 R-OH + 2 Na ---------> 2 R-O-Na+ + H2

Glassware : Test tubes, 5mL measuring cylinder

Materials : Ethanol (C2H5OH), isopropyl alcohol (C3H7OH), t-butyl alcohol (C4H9OH), Lucas reagent (mixture of concentrated hydrochloric acid and zinc chloride), chromic acid (H2CrO4), sodium metal.

Procedures:

A. Solubility of Alcohols

1. In three separate test tubes, about 1 mL of ethanol, isopropyl alcohol and t-butyl alcohol was added into each test tubes.

2. About 2 mL of water was added to each tube, mixed and observed.3. The experiment was repeated with two unknown liquids.4. The observation was recorded.

B. Lucas Test

1. Approximately 1 mL portions of ethanol, isopropyl alcohol and t-butyl alcohol was added in separate dry test tubes together with 6mL of Lucas reagent at room temperature.

2. The tubes was corked and shake. The time taken for the solution to turn cloudy or to form layered solution was noted.

3. The solutions that does not turn cloudy was heated in a hot water bath for few minutes and the observation was recorded.

4. The experiment was repeated with two unknown liquids.

C. Chromic Test

1. About 1mL of chromic acid was added into test tubes containing 2ml portions of ethanol, isopropyl alcohol and t-butyl alcohol each.

2. Observation on the colour change was recorded .3. The experiment was repeated with two unknown liquids provided.

D. Reaction with metallic sodium

1. In three separate dry test tubes, about 2mL of ethanol, isopropyl alcohol and t-butyl alcohol was added, then a small piece of sodium metal was inserted into the tubes.

2. Any visible changes in the solution was recorded.3. The different rate of gas evolution was compared and the alcohols was arranged in

increasing order of acidity.4. The experiment was repeated with two unknown liquids provided.

Hydrocarbons Ethanol Isopropyl alcohol

t-butyl alcohol Unknown A Unknown B

Solubility in water

Completely soluble in water

Completely soluble in water

Soluble in water

Soluble in water

Soluble in water

Lucas Test

No visible changes

Colourless solution turns cloudy upon heating in hot water bath

Immediate change to cloudy solution from colourless upon addition of reagent

Colourless solution turns cloudy upon heating in hot water bath

Immediate change to cloudy solution from colourless upon addition of reagent

Chromic acid Test

Reddish-brown solution turns to blackish-green solution with black precipitate

Reddish-brown solution turns to green colour solution with black precipitate

No visible changes

Reddish-brown solution turns to green colour solution with black precipitate

No visible changes

Reaction with sodium metal

Vigorous reaction with sodium metal.

Bubbles are released readily

Moderate reaction with sodium metal

Bubbles are released slowly.

Slow and calm reaction with sodium metal.

Bubbles are released in little amount

Moderate reaction with sodium metal

Bubbles are released slowly.

Slow and calm reaction with sodium metal.

Bubbles are released in little amount

Results:

Discussion:

The general formula of an alcohol is R-OH in which the R is an aliphatic hydrocarbon group. Alcohols may be looked upon as derivatives of water, H-OH. One hydrogen of water is substituted by an alkyl group, R. Like water, alcohols show hydrogen bonding. As the chain of the R group increases the hydrocarbon character of the compound overshadows the polar character of the OH group. Consequently, the solubility and boiling point of an alcohol are affected by the length of the carbon chain and the shape of the molecule. The short chain alcohols are soluble in water, whereas the longer chain alcohols are insoluble in water. In general a molecule which is more compact or highly branched will be more soluble in water and will have a lower boiling point than the straight chain isomer. Although alkyl alcohols have an -OH group, they do not ionize in water. The -OH group of alkyl alcohols can be positioned on different carbon atoms of the carbon chain and are classified as primary (1°), secondary (2°), or tertiary (3°) alcohols depending on whether the -OH group is attached to a carbon with 1, 2 or 3 other carbon atoms attached to it. [1][2]

In this experiment, the properties of alcohols were studies by treating the selected alcohol of different natures to be tested with several testing reagents. The alcohols used were ethanol as the primary alcohol, isopropyl alcohol as the secondary alcohol, and t-butyl alcohol as the tertiary alcohol. Besides that, two unknown liquids were given to be tested and the nature of the liquid was quest to be found.

Firstly, the solubility of the alcohols in water was tested. It was observed that all the alcohols was reasonably soluble in water as no layer of mixtures was found in any of the test tubes. This proves that all the alcohols are of simple compounds as the complex compound would be insoluble in water due to the long hydrocarbon chain.

Hydrocarbon Reaction equation Observation

Ethanol CH2H5OH(l) + H2O(l) → C2H5O-(aq) + H+(aq) Soluble in water

Isopropyl alcohol C3H7OH(l) +H2O(l) → C3H7O-(aq) + H+(aq) Soluble in water

t-Butyl alcohol C4H9OH(l) + H2O (l) → C4H9O-(aq) + H+(aq) Soluble in water

Unknown A - Soluble in waterUnknown B - Soluble in water

Secondly, Lucas test was carried out on all the alcohols provided. This test is used to distinguish among primary, secondary, and tertiary water soluble alcohols. Lucas reagent is a mixture of concentrated hydrochloric acid and zinc chloride. Zinc chloride is a Lewis acid, which

Ethanol Unknown B

Unknown A

t-butyl alcohol

Isopropyl alcohol

when added to hydrochloric acid makes it even more acidic. Water soluble tertiary alcohols react with Lucas reagent almost immediately to form an alkyl chloride which is insoluble in the aqueous solution. The formation of a second liquid phase in the test tube almost as soon as the alcohol initially dissolves is indicative of a tertiary alcohol. A secondary alcohol reacts slowly to form a chloride and, after heating a little, gives a second phase, usually within 10 minutes. Primary alcohols and methanol do not react under these conditions. In the case of tertiary alcohols the chloride is usually attached to the carbon that held the hydroxyl group. In the case of secondary alcohols, it is often the case that the chlorine is attached to the carbon that held the hydroxyl, but rearrangements are possible.[2]

When the alcohols are tested with Lucas reagent, the t-butyl alcohol and ‘Unknown B’ liquids reacts at instance by forming a cloudy solution. This proves that both the solution are of tertiary alcohol. On the other hand, isopropyl alcohol and ‘Unknown A’ liquid forms a cloudy solution only when introduced to heat, this prominently shows that the solutions are of the secondary alcohols. Ethanol unlikely to form any interaction with the Lucas reagent and proved to be primary alcohol.

Thirdly, the alcohols were tested with chromic acid. Generally, primary alcohols are oxidized to carboxylic acids by chromic acid. The Cr+6 ions in the chromic acid, which is red-brown, is reduced to Cr+3 ions, which is green in colour. Secondary alcohols are oxidized to

Ethanol Unknown B

Unknown At-butyl alcohol

Isopropyl alcohol

Addition of Lucas reagent: Before heating

Unknown A

Isopropyl alcohol

Addition of Lucas reagent: After heating

ketones by chromic acid. The chromium reduction is the same here as for the primary alcohols. Tertiary alcohols are not oxidized by chromic acid. Thus this reaction can distinguish between primary and secondary alcohols on one hand and tertiary alcohols on the other.[2]

When the samples was tested with Chromic acid, ethanol, isopropyl alcohol and ‘Unknown A’ shows a positive results where the orange colour of the chromic acid was changed to greenish blue-black solution with precipitate for ethanol and green solution with black precipitate for isopropyl alcohol and ‘Unknown A’ alcohol. This shows that oxidation reaction occurs and the alcohols are of primary and secondary alcohols. For t-butyl alcohol and ‘Unknown B’ alcohol, there are no visible change to the orange colour of the chromic acid, this indicated that there are no oxidation reaction took place and that the alcohols are of tertiary alcohols.

Finally, the alcohols was tested with sodium metal. Chemically, alcohols are only slightly weaker acids than water, with a K a value of approximately 1 × 10 −16. The reaction of primary

Unknown AIsopropyl alcohol

Unknown B t-butyl alcohol

Ethanol Unknown B

Unknown A

t-butyl alcohol

Isopropyl alcohol

alcohol, which in this experiments is ethanol with sodium metal, a base, produces sodium ethoxide and hydrogen gas.[3]

This reaction is identical to the reaction of sodium metal with water.

However, the this reaction occurs faster because of the increased acidity of water (K a value of 1 × 10 −15). The acidity of alcohols decreases while going from primary to secondary to tertiary. This decrease in acidity is due to two factors that is an increase of electron density on the oxygen atom of the more highly‐substituted alcohol, and steric hindrance due to the alkyl groups, which inhibit the dissolving property of the resulting alkoxide ion. Both of these situations increase the activation energy for proton removal.[3]

The basicity of alkoxide ions increases while going from primary to tertiary. This increase in basicity occurs because the conjugate base of a weak acid is strong. The weaker the acid, the stronger the conjugate base[3]

In this experiment, it is observed that ethanol produce a vigorous reaction and release of bubbles when introduced to sodium metal. The isopropyl alcohol and “Unknown A” alcohol produce a moderately fast eaction with sodium metal and bubbles release. In contrast, t-butyl alcohol and ‘Unknown B’ alcohol show very slow and calm reaction towards sodium metal and bubbles release. This shows, that the reactivity decreases from primary alcohol; ethanol, to secondary alcohol; isopropyl alcohol and ‘Unknown A’ and lastly tertiary alcohol; t-butyl alcohol and ‘Unknown B’

Several precautionary steps was taken while conducting the experiment. Following standard lab requirements, all students was ensured wearing lab coats, hand gloves and safety goggles. When handling the Lucas reagent, extra caution was taken as it is highly toxic and corrosive. The Lucas reagent was ensured to be handled in a fume chamber as the hydrochloric acid vapour is highly toxic to respiratory system. When handling the chromic acid, high precaution was taken to not to introduce any sodium to the acid as it produce a reaction with incandescence.

References :

1. Alcohol. (1997). In Compendium of Chemical Terminology, (The Gold Book) (2nd ed.). Online corrected version - (2006).

2. Properties of alcohol and phenol. (n.d.). Retrieved February 17, 2015, from http://employees.oneonta.edu/knauerbr/chem226/226expts/226_expt08_pro.pdf

3. (n.d.). Retrieved November 1, 2014, from http://www.cliffsnotes.com/sciences/chemistry/organic-chemistry-ii/alcohols-and-ethers/reactions-of-alcohols