You discover a set of three additional unknown compounds containing hydroxyl groups—Unknown Lily, Unknown Rose, and Unknown Poinsettia.
2. Unknown Lily is fast—quickly changing the orange-red of the chromic acid solution to a lovely turquoise, and turning Lucas reagent to milk in the blink of an eye without resorting to heat. Lily is, however, stumped by the Periodic test; no reaction here. What could the general classification of Unknown Lily be? Justify your choice briefly.
3. Unknown Rose is stubborn—chromic acid remains orange-red, and both Lucas and Periodic tests remain colorless, even given the gentle application of heat. What could the general classification of Unknown Rose be? Justify your choice briefly.
4. Unknown Poinsettia is an enigma—no change to the orange-red of the chromic acid solution, but producing modestly cloudy solutions with both the Lucas reagent (no heat) and the Periodic test. Not one of the six possibilities outlined in this experiment fits! Unless Poinsettia is a really strange compound, the most likely explanation is one of these three tests has generated bad data and should be repeated. Which test could this be? Assuming you've correctly identified the bad test result, what could the general classification of Unknown Poinsettia be? Justify your choice briefly.
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hemical Properties: The chemical behavior of the different classes of alcohols can be used as a means of identification. Quick, simple tests that can be carried out in test tubes will be performed. Please note that although the mechanisms of these reactions may be unknown to you, each of them is accompanied by definite visual changes (cloudiness, color change, etc.) which can be used in the "Real World" as well to identify substances. E.g.: The common "breathalyzer" used in determining whether a person is driving after ingesting too much alcohol contains an oxidizing agent which will change colors after oxidizing the ethanol to acetaldehyde and then to acetic acid exactly like the Chromic acid test explored in this lab. 1. Chromic acid test. This test (also described as Jones oxidation) is used to distinguish primary and secondary alcohols from tertiary alcohols. Using acidified dichromate solution, primary alcohols are first oxidized to aldehydes, and then further oxidized to carboxylic acids. Secondary alcohols are oxidized to ketones, which are resistant to further oxidation. Tertiary alcohols are not oxidized. In the oxidation, the orange-red of the chromic acid changes to a blue-green solution. Phenols are slowly (too slowly to notice much) oxidized to nondescript brown masses. O RCH2OH + H2Cr04 + H2SO4 RCOH + Cr2(SOA)3 green O RICHOH + HICr04 + H>SO4 RCR + Cry(SOA); green RICOH + H2Cr04 + + H2SO4 no reaction 2. Lucas Test. This test is used to distinguish between primary, secondary and tertiary alcohols. The reaction proceeds through a carbocation intermediate. The reagent is a solution of zinc chloride in concentrated hydrochloric acid, HCl. Tertiary alcohols react rapidly and give an insoluble white layer containing the corresponding alkyl chloride. A secondary alcohol reacts more slowly (within 15 minutes; slight heating may be required); and a primary alcohol does not react appreciably under these conditions. Benzylic alcohols, whether 10, 20, or 30, will also react rapidly as they can form a carbocation comparable to a 30 alcohol. The formation of an emulsion, cloudiness or milky solution is a positive test. Phenols will not react at all with the Lucas reagent. ZnC12 RCH2OH + HCI no reaction ZnCl2 ROCHOH + HCI - RICHCI + H20 (insoluble) ZnCl2 RICOH HCI RACCI + HO
a secondary carbon. If a carbon is attached to three other carbons then it is a tertiary carbon. Attachment to four carbons affords a quaternary carbon. For example, consider the following alcohols: CH3 CH, CH,OH CH;CHCH; CH,CCH, OH HO Ethanol Primary alcohol 2-Propanol tert-butyl alcohol Secondary alcohol Tertiary alcohol Two special types of alcohols will also be considered in this lab. The benzylic alcohol has the hydroxy group attached to a carbon which is also attached to a benzene ring, and the 1,2-glycol has two hydroxy groups on adjacent carbon atoms: OH OH HO Benzyl alcohol ethylene glycol Benzylic alcohol 1,2-glycol Phenols bear a close resemblance to alcohols structurally since the hydroxyl group is present. However, since the -OH group is bonded directly to a carbon that is part of an aromatic ring, the chemistry is quite different from that of alcohols. Phenols tend to be more acidic than alcohols. They do not give the characteristic reactions with chromic acid or Lucas reagents. Concentrated solutions of the compound phenol are quite toxic and can cause severe burns. Phenol derivatives are found in medicine: for example, thymol is used to kill fungi and hookworms. CH3 OH OH Phenol Thymol (2-isopropyl-5-methylphenol)
Reactions of Alcohols Purpose: In this assignment you will be given an unknown alcohol for which you will need to determine the general classification. Possibilities include six types: 10 alcohol, 2" alcohol, 3 alcohol, benzylic alcohol, 1,2-glycol, or phenol. The tools we will be using to perform this analysis include 3 of the functional group tests available: Chromic acid test (Jones oxidation), Lucas test and Periodic Acid test You will test the following known alcohols as references for comparison: benzyl alcohol (10 benzylic alcohol); 3-methyl-1-butanol (10 alcohol), tert-butanol (30 alcohol) and 2-methyl-1,2-butanediol (1,2- glycol). Background: Specific groups of atoms in an organic molecule can determine its physical and chemical properties. These groups are referred to as functional groups. Those hydrocarbons that contain the functional group -OH, the hydroxyl group, are called alcohols. Alcohols are important commercially and are used as solvents, drugs and disinfectants. The most widely used alcohols are methanol or methyl alcohol, CH:OH; ethanol or ethyl alcohol, CH3CH2OH; and 2-propanol or isopropyl alcohol, (CH3)2CH2OH. Methyl alcohol is found in automotive products such as antifreeze and "dry gas". Ethyl alcohol is used as a solvent for drugs and chemicals but is more popularly known for its effects in alcoholic beverages. Isopropyl alcohol, also known as "rubbing alcohol" is an antiseptic. Alcohols may be classified as primary, secondary or tertiary, depending on what kind of carbon the -OH group is attached to. If the hydroxyl group is attached to a primary carbon, then it is considered to be a primary alcohol. If the hydroxyl group is attached to a secondary carbon, then it is considered to be a secondary alcohol, and so forth. Classification of carbons depends on how many other carbon atoms it is attached to. If a carbon is not attached to another carbon, it is referred to as methyl. If it is attached to one other carbon then it is a primary carbon. If a carbon is attached to two other carbons then it is called
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