Chromic oxide tests

Chromic acid test. This test is able to distinguish primary and secondary alcohols from tertiary alcohols. Using acidified dichromate solution, primary alcohols are oxidized to carboxylic acids secondary alcohols are oxidized to ketones tertiary alcohols are not oxidized. (Note that in those alcohols which are oxidized, the carbon that has the hydroxyl group loses a hydrogen.) In the oxidation, the brown-red color of the chromic acid changes to a blue-green solution. Phenols are oxidized to nondescript brown tarry masses. (Aldehydes are also oxidized under these conditions to carboxylic acids, but ketones remain intact see Experiment 31 for further discussion.)... 

Chromic acid test. Aldehydes are oxidized to carboxylic acids by chromic acid ketones are not oxidized. A positive test results in the formation of a blue-green solution from the brown-red color of chromic acid. 

The chromic oxide content of the mixture at any time may be determined by titrating a test portion against standard ferrous ammonium sulfate solution. If the mixture is allowed to stand overnight at room temperature without stirring, it will be free from chromic oxide. A convenient procedure is to perform the oxidation in the afternoon and the extraction the next day. 

The chromic acid test for primary and secondary alcohols exploits the resistance of tertiary alcohols to oxidation. When a primary or secondary alcohol is added to the chromic acid reagent, the orange color changes to green or blue. When a nonoxidizable substance (such as a tertiary alcohol, a ketone, or an alkane) is added to the reagent, no immediate color change occurs. 

The solution from leather digestion can also be tested by AAA. Dilute the solution digested from the leather specimen from 125 ml to 1000 ml, then pipette 25 ml of the diluted solution to 250 ml for testing. Analyse the testing solution by the same AAA procedures described in Section 3.3.2. The chromium concentration (ppm) of the testing solution can be read directly from the instrument when the solution is pumped into the gas flame. The percentage of chromic oxide in leather can be calculated by the following equation ... 

American Society for Testing and Materials (ASTM) (1998), ASTM D28O7 Standard Test Method for Chromic Oxide in Leather (Perchloric Acid Oxidation). West Conshohocken, PA (reapproved 1998), ASTM. 

Alkylbenzenes can be distinguished from primary and secondary alcohols by their failure to give a positive chromic anhydride test. Recall, primary and secondary alcohols are oxidized by chromic anhydride, CrOs/ in aqueous sulfuric acid. Within two seconds, the clear orange solution turns blue-green and becomes opaque as shown ... 

Of various oxidants tested, hydroperoxide and chromic acid gave the best results (24% yield). 

A. Schrotter found that when dil. sulphuric acid sat. with hydrated chromic oxide is boiled for a long time and concentrated it furnishes a green soln. which is acidic to test-paper, and leaves on drying a green, amorphous mass from which... 

There are numerous other tests used to detect the aldehyde functional group. Most are based on an easily detectable oxidation of the aldehyde to a carboxylic acid. The most common tests are the Tollens, Fehling s, and Benedict s tests. Only the Tollens test is described in this book. The Tollens test is often more reliable than the chromic acid test for aldehydes. 

Note that a solution of chromic oxide in aqueous sulfuric acid (the Jones reagent) is used as a test reagent for 1° and 2° alcohols. A positive test is observed when the clear orange test reagent gives a greenish opaque solution upon addition of the alcohol (see Chapter 9). 

As indicated in the Discussion, a solution of chromic oxide in aqueous sulfuric acid is used as a test reagent for 1° and 2° alcohols. 

The reagent also reacts with primary and secondary alcohols (see Chromic Anhydride Test Jones Oxidation, p. 640). 

The relative ease of oxidation of primary and secondary alcohols compared with the difficulty of oxidizing tertiary alcohols forms the basis for a convenient chemical test. Primary and secondary alcohols are rapidly oxidized by a solution of CrOs in aqueous sulfuric acid. Chromic oxide (CrOs) dissolves in aqueous sulfuric acid to give a clear orange solution containing Cr207 ions. A positive test is indicated when this clear orange solution becomes opaque and takes on a greenish cast within 2 seconds ... 

Gldckner et al. [79] tested the stability of perfluorinated surfactants in acids or alkali under severe conditions. The 0.1% solutions of anionic surfactants in 60% nitric acid or 98% sulfuric acid containing 10 g/L chromic oxide were stored for a time span of 43 days, of which 28 days were storage at 90°C. The surface tensions of the anionic surfactants changed very little during the test (Table 4.10) [79]. 

Gluing is difficult, needing pre-treatments such as, for example, chemical etching (sulfo-chromic acid etching), flame oxidation or hot-air (500°C) treatment, corona discharge, plasma or UV treatments. The exposure must be brief and superficial and the original and aged properties must be tested. 

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