BMB222 – EX. 9

What is present in alcohols that makes these compounds more soluble in water than hydrocarbons?
The polarity of the hydroxyl group coupled with its ability to form hydrogen bonds.
Vanillin gives a purple color with ferric chloride solution. What part of the structure is responsible for the reaction that gives this test?
because it has a phenol group
Ethylene glycol is a liquid at room temp. and is soluble in water in all proportions. However, n-butane, CH3CH2CH2CH3, a compound of a similar molecular weight is a gas at room temp. and is insoluble in water. How do you account for these differences?
– Ethylene glycol has 2 OH groups, where hydrogens bond well with water and create high polarity.
– n-butane is a nonpolar hydrocarbon and does not have the same properties as Ethylene glycol (does not have OH groups).
Primary alcohols and secondary alcohols can be oxidized with chromic acid, but tertiary alcohols cannot. How do the structural differences between the alcohols account for the observed reactions?
– *Alcohols containing at least one alpha hydrogen are oxidized by chromic acid*, meaning tertiary alcohols are not oxidized by chromic acid.
– *Oxidation of a primary alcohol by chromic acid results in a carboxylic acid*, whereas, *oxidation of a secondary alcohol results in a ketone*.
How are phenols distinguished from alcohols?
– Phenols dissolve in aqueos NaOH, where alcohols with 6 carbon atoms do not.
– Phenols are alcohols with aromatic rings.
– Phenols are much stronger acids (more acidic) than alcohols.
– *You use ferric chloride or dissolve in a base to test and distinguish the two.*
How does the Lucas test work, what is it positive for, why is it used?
– add Lucas reagent (ZnCl2 in concentrated HCl), mix well by stoppering each test tube with parafilm and tap the test tube, allow to set for 5 minutes, look for cloudiness
– primary alcohols = nonreactive, secondary (slow reaction – usually after being heated) & tertiary (fast reaction) alcohols = white precipitate
– distinguishes primary alcohols from secondary & tertiary alcohols
How does the Chromic acid test work, what is it positive for, why is it used?
– add 10 drops of reagent grade acetone and 2 drops chromic acid, place test tubes in water bath for 5 minutes, note the color of each
– loss of the orange color and the formation of blue-green (teal) color is a positive test (primary and secondary alcohols produce teal color)
– distinguish primary and secondary alcohols from tertiary alcohols/phenols – primary alcohols oxidize to aldehydes, secondary alcohols oxidize to ketones, tertiary alcohols are not oxidized
Why are commercial alcohols important?
used as solvents, drugs, and disinfectants
What are the most widely used alcohols are…
– methanol or methyl alcohol, CH3OH – found in automotive products like antifreeze and “dry gas”
– ethanol or ethyl alcohol, CH3CH2OH – used as solvent from drugs and chemicals, but more known for its effects as an alcoholic beverage (primary alc.)
2-propanol or isopropyl alcohol (CH3)2CHOH – “rubbing alcohol” is an antiseptic (secondary alc.)
How does the Ferric chloride test work, what is it positive for, why is it used?
– addition of aqueous ferric chloride (yellow) to a phenol gives (depending on the structure) a green or purple color
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