Nitration Of Methyl Benzoate Biology Essay

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Alcohols, phenols, and ethers are organic derivatives of water mainly because of the similarity of their structure to that of water. Alcohol may be further classified to primary, secondary, and tertiary. All these compounds behave and react differently from each other under certain tests like Bayer's oxidation, chromic acid oxidation, ferric chloride test, and Lucas test. Ether showed negative reactions in all of the tests because of its strong bonding. Primary alcohols, secondary alcohols, and phenol are all oxidizable while tertiary alcohol and ether aren't. Ferric chloride test is a test for phenols hence, only phenols reacted positively in the said test. Phenols are more acidic than cyclic and acyclic alcohols. Tertiary alcohols on the other hand may be classified through the Lucas test. Secondary alcohol may also induce a positive reaction to the Lucas test but in a slower manner because it is less stable than the tertiary alcohol. In this experiment, there were 3 unknown samples. Unknown 1 was classified as primary alcohol, unknown 2 as ether, and unknown 3 as phenol. These organic derivatives of water are important because of its benefits for our health and uses for the economy

ABSTRACT

INTRODUCTION

Alcohols, phenols and ethers are organic derivatives of water mainly because of the similarity of their structure to that of water, as shown in figure 1.

Fig 1. Structure of water, alcohol, phenol, and ether

These compounds react in different ways making it possible to classify them through a series of tests. On the other hand, alcohol may be further classified based on the number of alkyl groups attached to the carbon that contains the hydroxyl group. (1)

Fig 2. Classification of alcohol

Again, these classifications have different behavior and reactions. Tests that could distinguish alcohol (primary, secondary, tertiary), phenol, and ether are Bayer's test, Chromic acid test, Lucas test, and Ferric chloride test.

MATERIALS AND METHODS (1)

Test tubes and Pasteur pipettes were the materials used for this experiment. Samples such as 1-butanol, 2-butanol, tert-butanol, phenol, diethyl ether, and 3 unknown samples were placed in separate test tubes (10 drops each) and were used to undergo tests like solubility in water, solubility in NaOH, Bayer's oxidation, Chromic acid oxidation, Lucas rest, and Ferric Chloride test. New samples were prepared for every test. For the solubility in water test, 10 drops of distilled water was added to each sample. 10 drops of NaOH were added for the solubility in NaOH test. In the Bayer's oxidation test, 10 drops of Bayer's reagent was added to the sample. For the chromic acid oxidation test, 10 drops of Na2Cr2O7 together with 6 drops of concentrated H2SO4 was added to the sample. 20 drops of Lucas reagent was used for the Lucas test. The reaction was observed for 5-10 minutes. Lastly, 10 drops of ferric chloride was added to the sample for the ferric chloride test. All reactions were observed after shaking in every test. The results of the reactions of the 3 unknown compounds were compared to that of the known compounds for classification.

RESULTS AND DISCUSSION

Below are tables representing the data that were gathered throughout the experiment.

Table 1. Solubility and Reaction Profile

Solubility in H2O

Solubility in NaOH

Bayer's Oxidation

Chromic Acid Oxidation

Lucas Test

Ferric Chloride test

Classification

Visible+result

No layer formed

No layer formed

Brown ppt

Green blue color

Cloudiness

Brown/black/ purple color

SAMPLES

Ethanol

++

++

+

++

-

-

2-Butanol

+

-

+

++

+

-

Tert-butanol

+

-

-

-

+

-

Phenol

-

++

++

+

-

+

Phenol

Diethyl ether

-

+

-

-

-

-

Ether

Unknown 1

-

-

++

++

-

-

Unknown 2

-

-

-

-

-

-

Ether

Unknown 3

++

++

++

+

-

+

Phenol

Legend: ++→fast reaction; + → slow reaction; - → no reaction

IDENTITIES OF UNKNOWN SAMPLES

Sample 1: Primary alcohol

Sample 2: Ether

Sample 3: Phenol

Bayer's test and Chromic acid test are both tests for oxidation. Both are tests for phenols, primary, and secondary alcohols which are all oxidizable compounds. On the other hand, tertiary alcohols cannot be oxidized because of the absence of the hydrogen attached to the alcohol carbon. Oxidation is a process where hydrogen atoms are removed from the alcohol. (2) Bayer's test requires the use of the reagent KMnO4 or potassium permanganate which is normally deep purple in color and will turn into a brown precipitate if the compound that is tested is oxidizable. The chromic acid test was done with a chromic acid reagent which is a combination of Na2Cr2O7 and concentrated H2SO4. The reagent is originally yellow orange in color and a positive reaction would induce a color of green/blue.

Fig 3. Primary and Secondary Alcohol reaction under Bayer's test

Primary alcohols when oxidized produce aldehyde or carboxylic acid. It is based upon the reaction conditions. If the product is a carboxylic acid, that means that the alcohol was first oxidized to aldehyde and was then further oxidized to a carboxylic acid (3). Secondary alcohols on the other hand would have ketone as a product. Unlike primary alcohols, it wouldn't be possible to produce carboxylic acid out of secondary alcohols because the oxygen slotted between the carbon and hydrogen (refer to the structure of aldehyde in fig.3) is not present. Meanwhile, phenols would also have a positive reaction because it is also oxidizable. However, phenols can only be oxidized by strong oxidizing agents (1) and they can't be oxidized into aldehydes or ketones. Phenols that undergo oxidative de-aromatization or Teuber reaction produces quinones. Diphenol will be produced if it undergoes Elbs presulfate oxidation (4). Phenols are also said to be more acidic than alcohols because of the increase in electron density around the ring which is caused by the donation of the oxygen's lone pair to the ring system. It also helps to make the -OH group's hydrogen be more acidic. (5)

Lucas Test is a test for tertiary alcohols. It is done with the lucas reagent which is a combination of ZnCl2 and concentrated HCl(6) . This test shows a substitution reaction wherein a Cl atom replaces the -OH group. Both tertiary and secondary alcohols resulted to a positive reaction in this test.

Fig 4. Secondary and Tertiary alcohol reactions under Lucas Test

Both of these reactions went through the Sn1 (unimolecular nucleophilic substitution) mechanism which involves a carbocation intermediate. Firstly, the -OH ion will be removed from the alcohol and the Cl ion will add to the positively charged carbon atom (refer to fig. 5). The reason behind the 5-10 waiting time in the lucas test is because secondary alcohols would take a longer time to react compared to the tertiary alcohols which is much more stabilized. Primary alcohols would therefore not react because its primary carbocation is very unstable. (7) Cloudiness of the sample after shaking would indicate a positive reaction.

Fig 5. Mechanism for the nucleophilic substitution of tertiary alcohols + Lucas reagent

Ferric Chloride test on the other hand is a test for phenols. As what Table 1 has shown, only phenol and unknown 3 has resulted to a positive reaction for the test. The ferric chloride reagent's original color is yellow orange and will change to brown, black, or purple for positive reaction. Ferric chloride reagent has ions that form color complexes with several organic compounds, and one which is phenol. Every compound may vary in the color of the complexes (8). Alcohols however do not form color complexes with Fe3+ ions thus if there is no presence of color change, then phenol is not present in the sample.

Fig 4. Phenol under Ferrich chloride test

Below is a table that would summarize the reactions of a primary alcohol, secondary alcohol, tertiary alcohol, phenol, and ether.

Bayer's test

Chromic acid test

Ferric Chloride test

Lucas Test

Primary ROH

+

+

-

-

Secondary ROH

+

+

-

+(slow)

Tertiary ROH

-

-

-

+

Phenol

+

+

+

-

Ether

-

-

-

-

Table 2. Summary of the reactions of the samples under diff. chemical tests

Notice that ether didn't result to any positive reaction in all the tests. This is because ethers are unreactive or inert and have a very stable bonding. This property of ethers is the reason why they are commonly used as solvents. Alcohols are also used as solvents, starting materials, cosmetics and antifreeze. Phenols are used as disinfectants and antioxidants (9). This antioxidant property of phenol is very beneficial to our health. According to studies, polyphenols which are found in plant foods may lower the risk of cancer. Another study is about plant derived polyphenols which shows that these compounds can possibly slow down the spread and growth of cancer cells. Polyphenols are said to trigger a series of reactions that may lead to apoptosis or a process of self-destruction of these cells. Polyphenols also has the ability to increase NO bioavailability. The increase in NO-cyclic GMP pathway explains the beneficial effect of flavonoids at vascular level. (10)

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