(Procedure B)
2 drops of ammounium polysulphide solution was added to 2 ml of the stock solution. The mixture was evaporated to dryness on a steam bath. Then 5 ml of dilute hydrochloric acid was added, the solution was warmed and filtered. A few drops of ferric chloride solution was added to the filtrate. A red coloration would be observed if nitrogens is present.
Detection of halogens (if Nitrogen is absent)
2ml of the other portion of the filtrate in “sodium fusion test” was acidified by dilute nitric acid. Silver nitrate was added and the result of the reaction was observed.
Procedure for determination of the solubility properties of the compound
Different kinds of solvents were used to mix with each of the unknown compounds, and the miscibility were observed. 3.0ml of the solvent was slowly added to 0.3 g of the compound in a small test tube. The mixture was shaken vigorously and the solubility was observed and recorded. If the compound was soluble in the solvent, no separate layers will be formed while two layers will be formed or suspensions were observed if the compound was not soluble in the solvent.
Procedure for Spectroscopic analysis
About 15 to 20 mg of the unknown solid was ground in an agate mortar, and then a drop of the paraffin oil was added, and was ground for 2 to 5 minutes until a mull was formed. The mull was transferred to the bottom salt plate of a demountable cell. For the liquid sample, one drop of the sample was directly added to the salt plate. The top plate was then placed and twisted to distribute the sample evenly and eliminate all air pockets and the spectrum was run. After running the sample, the salt plates were wiped clean with a tissue paper saturated with chloroform.
Procedure for Chemical characterization tests
For BS:
2,4- dinitrophenylhydrazine test
0.05 g of the unknown solid, 2 ml of reagent grade 95% ethanol and 1 ml of 2,4- dinitrophenylhydrazine reagent were mixed in a test tube, and being shaken vigorously. The test tube was heated if necessary. 5 drops of distilled water were added to the mixture afterwards. Formation of a yellow precipitate showed the presence of carbonyl group.
Ferric chloride test
0.02 g of the unknown solid was dissolved in 1 ml of water and poured the resulting solution into a small test tube. One drop of a 5 % aqueous solution of ferric chloride was added to the dissolved organic compound and the colour of the resulting solution was observed. Formation of red, green, blue or purple complexes indicated that the sample was phenol.
For BL:
Hydroxamate test for carboxylate esters
2 drops of the unknown liquid were added to 1 ml of 1M hydroxylamine hydrochloride in ethanol. Then, a 15 % ethanolic solution of potassium hydroxide was added dropwise until the test solution was just basic to pH test paper. Additional five drops of the solution were added. The mixture was heated to boiling for 30 seconds and was allowed to cool to room temperature. With thorough mixing, an aqueous solution of 10 % of aqueous hydrochloric acid was added dropwise until the pH of the mixture is approximately 3. Two drops of the 5 % aqueous ferric chloride were added and the colour change was noted. Formation of red-blue or violet colour indicated that the orginal compound was an ester.
Procedure for Literature search
The physical and the spectroscopic properties of the unknown compounds with compounds of the same chemical class were compared. The properties with the literature values stated in the data books were compared in order to futher deduce the structure of the unknown.
Results
Preliminary physical test
For BS, the unknown solid appear to be white pale orange watery needle-shaped crystals which are thin, short and pointed solid. It has an acrid smell. For the ignition test, it melted first and then burned with orange and sooty flame.
For BL, the unknown liquid is colourless. For the ignition test, it burned with a blue flame.
Qualitative Analysis of Elements
For the detection of nitrogen of procedure A, both the BS and BL unknown showed a negative result. No Prussian blue precipitate was present. For the detection of nitrogen of procedure B, both of them also showed a negative result. No red coloration was found. Therefore, both of them do not contain nitrogen.
For the detection of halogens, both the BS and BL unknown gave a negative result. No observable changes were observed and there were no formation of precipitate. Thus, halogen was absent in both unknown samples.
Solubility test
For BS, it does not dissolve in water and HCL, but it dissolves in NaOH and gives a pink colour. It is also not dissolve in NaHCO3. Thus, BS is class A2 which may be phenols or some acids and anhyrides.
For BL, it does not dissolve in water, HCL and NaOH, but it dissolves in H2SO4 and gives out a light yellow. Therefore, it is class N which may be alcohol, aldehydes, ketones, esters, ethers, unsaturated hydrocarbons or anhydrides.
IR spectroscopy
For BS, in the spectrum, there were a broad peak at 3384 cm-1 which indicated the presence of OH group for phenol, a little small peak at 3000 cm-1and peaks occurred at 910-1377 cm-1 indicating there is aromatic ring, peaks at 2852 cm-1 and 2923 cm-1indicating the presence of CH3 and CH2 groups. Two strong and sharp peaks were found at 727 cm-1 and 759 cm-1 indicating that the aromatic ring are o-disubstituted.
For BL, in the spectrum, there were sharp peak at 2985 cm-1 indicating the presence of CH3 and CH2 groups, a strong ad sharp peak at 1741 cm-1indicating the presence of C=O bond, peak at 1047 cm-1 and 1241 cm-1which is stronger and boarder indicating the presence of C-O bond for ester.
Chemical characterizations test
For BS:
The result of 2,4- dinitrophenylhydrazine test was negative. No formation of orange-red ppt was found while in ferric chloride test showed a positive result as red complex was formed.
For BL:
In the hydroxamate test, after the addition o ferric chloride , a reddish brown colour was formed. The result was between positive and negative. When this test was repeated, a red-blue colour was formed which was a positive result.
Discussion
For the ignition test, as BS burned with orange and sooty flame, we could first deduce that it may be aromatic hydrocarbon which has a relatively high carbon content while for BL , we could deduce its oxygen content is high as it burned with a blue flame.
From the results of nitrogen test, both the results of procedure A and B for BL and BS were negative. Therefore , we could confirm that they both do not contain nitrogen. And for the halogen test, both the BS and BL unknown gave a negative result. No observable changes were observed and there were no formation of precipitate. Thus, halogen was absent in both unknown samples. At this stage, we knew that both BS and BL do not contain any nitrogen and halogens.
After the solubility test, as we already knew that BS and BL do not contain any nitrogen and halogens, we could deduce that BS is class A2 which may be phenols or some acids and anhyrides. And for the solubility result of BL, we could deduce BL is class N which may be alcohol, aldehydes, ketones, esters, ethers, unsaturated hydrocarbons or anhydrides.
After IR spectroscopy, in the spectrum of BS, there were a broad peak at 3384 cm-1 which indicated the presence of OH group for phenol, a little small peak at 3000 cm-1and peaks occurred at 910-1377 cm-1 indicating there is aromatic ring, peaks at 2852 cm-1 and 2923 cm-1indicating the presence of CH3 and CH2 groups. Two strong and sharp peaks were found at 727 cm-1 and 759 cm-1 indicating that the aromatic ring are o-disubstituted. Therefore, combining the results from previous tests and the molecular mass of BS (122 g), we could deduce that BS is a phenol containing an aromatic ring and around two substituted group.
For BL, in the spectrum, there were sharp peak at 2985 cm-1 indicating the presence of CH3 and CH2 groups, a strong ad sharp peak at 1741 cm-1indicating the presence of C=O bond. There were peak at 1047 cm-1 and 1241 cm-1 and one band was stronger and boarder than the other meaning the present of C-O group of esters. Therefore, combining the results form previous tests and the molecular mass of BL (88 g), we could deduce that BL is a carboxylate ester.
Further chemical characterizations test was done to confirm the deduction.
For BS, the result of 2,4- dinitrophenylhydrazine test was negative while in ferric chloride test showed a positive result as red complex was formed. We could confirm that it is phenol. For BL, positive result of hydroxamate test could confirm that BL is carboxylate ester.
For all the steps above we could nearly confirm that BS was dimethlphenol and BL was ethyl acetate or methyl propionate. However, we could not determine the exact linking position. For example, it is difficult to deduce the exact position of the two subsitituted group of BS without checking in the data book as it can be
2, 4-dimethylphenol or 2, 3- dimethylphenol. However, all of the isomers have different b.p.and m.p., so the only way to identify which one is the answer can be only done by comparing the b.p. and m.p. with the literature value of all their isomers in the data book.
The physical and the spectroscopic properties of the unknown compounds with compounds of the same chemical class were compared. For BS with the given molecular mass of 122.17 g, the only possibilities found in data book were C4H10O4, C6H2O3 and C8H10O. As we knew that BS has aromatic ring and is a phenol, the only suitable structure is C8H10O which have 2 CH3 substituted group. Thus, from the data in the data book, it could be 2,4-dimethylphenol(m.p.22-23。C), 2, 3- dimethylphenol
(73-75。C), 2,5- dimethylphenol(75-77。C), 2,6-dimethylphenol(46-48。C),
3,4- dimethylphenol(46-48。C) or 3,5- dimethylphenol(65-66。C). As it was given that the m.p. of BS is 22-23。C, only one possibility matched which are 2,4- dimethylphenol.
For BL with the given molecular mass of 88.11 g, the only possibilities found in data book were C3H4O3, C4H8O2, C5H12O. As we already knew that it is carboxylate ester, the only suitable formula is C4H8O2. For this formula , there are only two possibilities which are ethyl acetate and 2-methyl propionate. By comparing the b.p. of BL and the literature value of these two possibilities in the data book, BS is ethyl acetate which b.p. is 76-78。C rather than 2-methl propionate which b.p. is 79。C. In fact, both the b.p of ethyl acetate and 2-methyl propionate are so near. However, the most approximate one was ethyl acetate, so we chose ethyl acetate.
Source of errors and improvement
For the IR spectrum of the unknown BL and BS, some sharp unnecessary peaks might appear to interfere with our deduction .This might due to the contamination of the unknown compounds or the present of impurities .Moreover, we used chloroform to clean the plate which might not evaporate completely before we put them in the spectroscopy. For improvement, wait for a while after cleaning the salts plates or apparatus used for IR spectroscopy so that the chloroform can fully evaporate in order not to interfere the results. All the unknown samples must handle carefully such as using a new dropper or spoon to take the sample out each time to reduce contamination chance to minimum. More Chemical tests can be done to further confirm the results.
For the result of hydroxamate test for carboxylate ester, the first time result was between positive and negative. This might due to the present of impurities or the improper amount of the reactant used. Too much addition of ferric chloride for the last step of the test might also interfere with the result colour as it is yellow in colour. For improvement, make sure all the apparatus used are clean and the test can be done for one or two more times. Proper amount of the reactant is used and at most 3 drops of ferric chloride are added at the last step so that it will not cover the resultant colouration.
Conclusion
The given unknown solid BS with molecular mass of 122.17 g and m.p. of 22-23。C was 2, 4-dimethylphenol and the unknown liquid BL with molecular mass 88.11 g and b.p. of 76-78。C was ethyl acetate.
