UNIVERSITY BRANDEIS CHEMISTRY 29A PRELAB WRITEUP AND EXPERIMENTAL REPORT SHEET NAME_ T.A.S NAME _________ EXPERIMENT # __7_____ TITLE Ketone Identification Purpose: to characterize an unknown carbonyl compound using BP analysis, MP derivative analysis, NMR and IR spectra analysis PRELIMINARY WRITEUP* (INCLUDING EQUATIONS, TABLE OF MATERIALS, THEIR AMOUNTS AND CONSTANTS. AND PRELAB QUESTIONS. Place these questions on the reverse of this page) (* use reverse of both sheets if necessary) Substance Purpose Melting Point Other (Celsius) notes Water Solvent, cleaning agent, catalyst in multiple reactions N/A Sodium hydroxide Reacts with iodine and aldehyde or methyl ketone to form iodide ion and N/A carboxylic acid anion Iodine solution Source of iodine for reaction in iodoform test, the iodine turns into the iodide N/A ion in presence of hydroxide and an aldehyde or methyl ketone, the yellow insoluble iodide provides the positive test 1,2 dimethoxymethane Solvent for water insoluble ketones in iodoform test N/A Phosphoric acid Catalyst for DNP reaction with aldehyde N/A Unkown aldehyde (2,3The unknown N/A pentadione) 2,4 dinitrophenylhydrazine Substance which reacts with the aldehyde or ketone via a condensation N/A reaction forming an imine, an insoluble compound Schiffs reagent Tests for presence of aldehyde, by color formation N/A Methylene chloride Cleaning IR plates, and IR solvent N/A Trichloro dutero methane NMR solvent N/A TMS NMR reference compound N/A Nitrogen gas Purging oxygen from NMR samples N/A EXPERIMENTAL PROCEDURES* MODIFICATIONS AND OBSERVATIONS* (include in preliminary writeup) (Obtained from the lab experience.) Iodoform test 1. if unknown is water soluble dissolve 4 drops of liquid or The iodoform tested yielded positive results for formation of 50 mg of solid in 2mL of water yellow insoluble compound for both number 82 (the aldehyde) and 2. if unknown is not water soluble dissolve it in 2 mL in 1,2 a positive control. The ketone was insoluble in water, but the first dimethoxymethane test was carried out in water anyway, it formed a cloudy white 3. add 2 mL of 3M sodium hydroxide solution that was incorrect. After salvation of the ketone with 4. slowly add 3 mL of iodine solution dimethoxymethane, the clear solution or negative result was 5. dilute to 10 mL with water if ketone was insoluble in observed for number 233. After addition of schiffs reagent to the water test tubes the aldhyes rapidly turned dark purple, the positive 6. observe results of reaction control (acetone) and sample 82 were both the same color while Schiffs test 233 was not dark purple. The ketone smelled like a strong sweet 1. add 3 drops of unknown to 2 mL of Schiffs reagent smell, similar to bananna. The measured boiling point of 233 was 2. allow 10 min for the reaction 126 degrees Celsius. The DNP in acid was a dark red/orange color, DNP synthesis after addition of carbonyl a colored yellow/orange solid formed. As 1. add 0.05g of unknown to 5mL solution of 2,4 the solution was heated and allowed to react and cool a darker reddinitrophenylhydrazine in phosphoric acid orange solid crystallized out of solution. This product appeared 2. warm reaction for 1-3 min, then allow to air cool uniform in color and moderately pure; the measured melting point 3. help crystallization by ice cooling was 71 degrees Celsius. A large amount of product was collected in 4. collect crystals by suction filtration suction filter and subsequently dried. 5. wash crystals with large excess water to remove phosphoric acid, until litmus paper does not read as acidic 6. dry further with filter paper 7. determine melting point
RESULTS, DISCUSSION AND CONCLUSIONS* To determine that the compound I was testing was indeed an ketone I utilized 2 different tests, the iodoform test and the schiffs test. The iodoform test relies on. Certainly, if this test is positive it is reasonable to suspect the unknown compound is an aldehyde or methyl ketone, and if it is negative it is reasonable to suspect a ketone. In the test unknowns, 82 was positive and 233 was negative, therefore we can be sure 233 is not an aldehyde or methyl ketone but 233 requires further testing to determine its structure. These results were consistant with the positive control (acetone) used. The schiffs test was also carried out and it relies on the ability of a colorless reagent (schiffs reagent) to react with an aldehyde and produce a magenta color. This test is also only semi definitive for aldehydes because air oxidation alone can turn the solution pink given enough time, just as importantly even small contamination in the test (for instance the acetone used to clean most glassware) will generate a false positive result. In the tested unknowns, 82 was also positive and 233 was negative for this test. The addition of 2 semi definitive tests yielding the same result for compound 233 confirms that this compound is likely an not an aldehyde or methyl ketone and further spectrographic and derivative analysis can be then undertaken. These results were consistent with the positive control (acetone) used. The methyl ketone test eliminates 4-Methyl-2-pentanone, 2,4-Dimethyl-3-pentanone, and 4-Methyl-3-penten-2-one because they are methyl ketones. The boiling point for this ketone gives a set of possible compounds due to a +- 10 degree range. See chart on back. The boiling point test for a compound is reliable with this small range and can be used to eliminate many compounds from possibility. The next step in synthesis of a derivative for melting point analysis, to help narrow down the possibilities. Synthesis of the 2,4dinitrophenylhydrazine compound (sometimes called a carbonyl test), relies on the ability of a carbonyl compound to react (by nucleophillic addition) with a NH2 amine to form a CN double bond (imine) attaching the two different molecules. The primary amine in this case, the 2,4-dinitrophenylhydrazine reacts with the carbonyl group by mechanism of a hemiaminal dehydration until the imine forms, a form of condensation, and requires acid catalysis to occur. This test is reliable for identifying a carbonyl compound, however it is difficult to achieve significant discrimination between different imine derivatives because melting point determination and analysis is unreliable. The next step for carbonyl analysis is spectrographic analysis to fully determine the nature of the compound. Spectrograpphic analysis is highly specific in that most compounds have a unique set of IR, HNMR and C13NMR charts; however said analysis is not always simple. The IR peaks only give basic bond possibilities, for C-H bonds it is difficult to determine anything more than that a C-H alkane, alkene or aromatic exists. For the carbonyl bonds the IR peaks are most useful and accurate because of the small ranges for possible resonance, in the ketone the value of 1709 was within the range for only a saturated ketone. This eliminates the 5-Hexen-2-one because it is unsaturated. Here we must continue to HNMR and C13NMR to fully determine the structure of the compound. HNMR and C13NMR are tests that are undertaken to largely confirm and quantitatively characterize compounds, the HNMR gives the electronic environment of all of the hydrogens in the compound and the C13NMR does similar for the carbons. NMR does this my placing odd numbered atoms in a strong magnetic field, and collecting data (usually charged coupled devices) on the energy states of the odd numbered atoms (odd numbered atoms each have 2 different energy states while in a magnetic field). The electrons surrounding the atoms influence these energy states. While these NMR results are highly reliable (as long as all solvents and the compound are pure) they are not the first choice for characterization due to difficulty in interpreting some highly coupled patterns. However if sufficient time and resources are invested for the NMR data collection, different patterns for different magnetic field strength can be collected and result in a highly reliable technique. Here the HNMR and CNMR eliminated the 2,3-pentadione from possibility because the cyclo compound only has 2 different types of hydrogen (in 1:1 ratio) and only 3 types of carbon, neither of these results are present in the spectrographic results. While all of these previous techniques can determine the structure of most compounds, there are certain highly complex and extremely large aldehydes and ketones (large organic molecules, proteins, etc) that cannot be resolved by any of these previous techniques, for those X-ray crystallography is the primary analysis tool. In conclusion the unknown was ketone as characterized by iodoform and Schiffs test, derivative melting point analysis, boiling point analysis, and spectroscopic techniques and is 2,3-pentanedione. ANSWERS TO END-OF-CHAPTER QUESTIONS* 8. The 2940 vibration is from a c-h stretch from an alkane c-h bond, this is present in here
9. the carbonyl peak is at 1730 indicating a saturated ketouyhjne 10. the triplet a 1.0 is due to 3 hydrogens interacting to a CH2. The singlet at 2 is due to 3 hydrogens interacting with a CO carbonyl. The quartet at 2.5 is due to 2 hydrogens interacting with both a CO carbonyl and a CH3 group.
Possible Compounds (Based on boiling point) for the ketone Boiling Point (Celsius) Compound semicarbazone melting point (Celsius) 114116 4-Methyl-2-pentanone 132 124 128129 129 130131 2,4-Dimethyl-3pentanone 5-Hexen-2-one 4-Methyl-3-penten-2-one Cyclopentanone 160 102 164 210
DNP melting point (Celsius) 95 88.95 108 205 146
133135 2,3-Pentanedione 122 (mono) 209 For IR values the only relevant value was the spike at 1709 (a saturated ketone), the other results (the erroneous 3055 alkene) and other alkane values were not needed because a more accurate method (NMR) overruled these indications.
Sodium hydroxide
Phosphoric acid
2,4 dinitrophenylhydrazine
Iodine
Schiffs reagent
Methylene chloride
Trichloro dutero methane
TMS
Nitrogen gas
2,4 dinitrophenylhydrazine