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Lab 1: Identification of Unknown Organic Compounds by MP, BP, and Infrared Spectroscopy Zeba N. Siddiqui (Partner: Keti Berberi) September 11, 2014

Methods and Backgrounds: The purpose behind this lab is to practice safety when following protocols. A secondary goal is to learn the techniques of melting points, boiling points and infrared spectroscopy and use them to identify unknown organic liquid and solid compounds. The melting point is the point where a solid would melt. It is psychical property defined as the temperature at which the phases of a liquid and solid occur in equilibrium without an alteration of temperature. With saying that, the sample would not liquefy at a single temperature point, however, over a temperature range in which the solid begins to melt and then is transformed into a liquid. If the crystalline sample is pure, then it should liquefy over a narrow or sharp range. The start of a solid melting is characterized as a softening, which describes the shrinking of the solid sample. However, it is not always possible to observe this softening, so the use of a range is appropriate. For example, Sample 1 of an experiment is recorded to melt at 115◦C. That would be an improper number, a range is needed at, for example, 114-116◦C. A common method to determine melting point is the use of a capillary tube. In this methods, an organic solid is placed in the capillary tube. The tube is then placed into a larger tube to allow the solid to move towards the bottom of the tube. After the solid has gathered, the tube is placed into a melting apparatus where the solid melts. This allows the observation of the melting point of the solid sample. Boiling point, on the other hand, is the temperature at which a liquid boils and transforms to vapor. It is the temperature at which the vapor pressure of the liquid compound is equal to the

external pressure surrounding that compound. Similar in a sense like melting point, boiling point is stated as the range at which a liquid sample begins to evaporate. This can be measure by placing a sample of an organic compound into a test tube. A thermometer is used to measure the temperature, which rests just above the liquid and is fastened to a stand. Boling point is a physical property, like melting point, that is used to determine an unknown liquid organic sample based on its boiling point temperature range. Infrared (IR) Spectroscopy is the absorption of infrared waves. IR Spectroscopy determines the different functional groups within an unknown sample and used as a comparison. The peaks on the spectrum identify the specific functional groups, for each functional group have different peak numberings. Figure 1 represents the IR Spectroscopy of the structure Vanillin.

Figure 1 The IR spectrum of Vanillin.

Experimental Procedures: Part 1: Unknown Organic Liquid (P) First, it is needed to obtain the sample from the hood and placed into a test tube and set it aside. The procedure can be done in any order, so order does not matter in which the experiment is conducted. Molecular formula determination is one of the four steps needed to identify the

unknown organic compound, P. To determine the molecular formula of unknown P, one must use empirical analysis and molecular weight first. As given in Unknowns: Table of Elemental Analysis and Molar Mass from Organic Chemistry: Lab Manual and Course Materials, found in Table 1, the percent at which an unknown contains carbon, hydrogen, oxygen, and nitrogen molecules along with its molar masses. The given molecules are used to determine both empirical and molecular formulas. Once the formulas are determined, the given molar mass divided by the empirical molar mass would equal to the molecular formula, which should result in one. Another step is the Index of Hydrogen Deficiency (IHD) determination. This determines the number of possible combinations of double and triple bonds and rings. Unknown P contains only carbon, hydrogen and oxygen molecules. The necessary formula, Hydrocarbons (CnHx) and Oxygenates (CnHxOy), will determine the combination of bonds, this can be found in Table 6. A third step is the Fourier Transform Infrared (IR) Spectroscopy. Place a small amount of the unknown liquid sample into the small circle on the machine, after cleaning it off with ethanol to prevent a false reading. Place a covering on it and let the machine read the peaks. Figure 1 is an example of the image that can be produced. The peaks will determine which functional groups are present in unknown P, which can be found in Table 2 and Table 6. The last step, other than the structure elucidation (the naming), is the boiling point determination. Prepare the stand with the heating apparatus. Next, place about two inches of the unknown liquid sample, P, into a test tube. Clamp a thermometer, with a rubber ring, just above the liquid sample. The thermometer must not touch the sample and the test tube must not touch the heating apparatus. Then turn on the heating apparatus to 40◦C at the start, then gradually increase. Mark

the first bubble that appears until the actual boiling, this will consist of the boiling range. Repeat the process for a more accurate range of the boiling point. Results are found in Table 4.

Part 2: Unknown Organic Solid (O) Just like the unknown liquid sample, obtain the sample from the hood and placed into a watch glass, instead of a test tube, and set it aside. Again, the procedure can be done in any order, so order does not matter in which the experiment is directed. Molecular formula determination is one of the four steps needed to find the unknown organic compound, O. The same method applies for both the unknown organic solid and liquid samples. Numbers are found on Table 1. The other step, like before, is the Index of Hydrogen Deficiency (IHD) determination. This determines the number of possible combinations of double and triple bonds and rings. Unknown O, however, contains carbon, hydrogen, oxygen, and nitrogen molecules. The necessary formula for compounds with nitrogen (CnHxNy), this can be found in Table 6. Just like the third step, the IR Spectroscopy, for the liquid sample, the solid sample is the same, however, the procedure has one difference. Place a small amount of the unknown solid sample into the small circle on the machine, after wiping it off with ethanol to prevent any incorrect reading. The difference is to not place the covering on the solid sample, but to place a needle over it, then allow the machine to read the peaks. Again, Figure 1 is an example of the image that can be produced. The peaks will determine which functional groups are existing in unknown O, which can be found in Table 3 and Table 6. The last step, besides the structure elucidation, is the melting point determination, instead of the boiling point. Using a capillary tube, scope some of the solid sample and place it into the MelTemp heating apparatus. As a first test, increase the temperature drastically. Note when the start

of the melting begins and when the solid has completely liquefied, this would be the melting range. Another test should be taken for better accuracy, for the drastic increase will not mark at the exact temperate. In the second run, start 10◦C lower than the start of the melting in the first trial, then gradually increase the temperature. Again, mark the start and the end as your melting range. The results are found in Table 5. Unknown

Carbon (C)

Hydrogen (H) Oxygen (O)

Nitrogen (N)

Molar Mass (g/mol)

O (solid)

71.09%

6.71%

11.84%

10.36%

135.068

P (liquid)

64.82%

13.60%

21.59%

0%

74.073

Table 1 Unknowns: Table of Elemental Analysis and Molar Mass

Data Acquisition Equations: Elemental Analysis + Molecular Weight  Molecular Formula 1. Convert percent into moles: Moles (grams) (assume percent are moles) = moles Molar Mass (grams/mole) 2. Normalize-Divide by smallest value: Moles found in step 1 .=# Smallest mole value form step 1 3. Multiple by integers if necessary: C#H#O#N# 4. Divide given MW by empirical MW. IHD = (2n +2) – X 2 Calculations:

IHD = (2n+2) – (X+Y) 2

Unknown Organic Liquid, P:

Elemental Analysis + Molecular Weight  Molecular Formula 1. Convert percent into moles: C: 64.82g = 5.4mol 12g/mol

H: 13.60g = 13.6mol 1g/mol

O: 21.59g = 1.35mol 16g/mol

2. Normalize-Divide by smallest value: C: 5.4mol = 4 1.35mol

H: 13.6mol = 12 1.34mol

O: 1.35mol = 1 1.35mol

3. Multiple by integers if necessary: C4H10O X 1 = C4H10O 4. Divide given MW by empirical MW: Given MW = 74.073g/mol = 1 Empirical MW 74 g/mol IHD = (2n +2) – X = [(2 X 4) – 10] = 0 2 2 Unknown Organic Solid, O: Elemental Analysis + Molecular Weight  Molecular Formula 1. Convert percent into moles: C: 71.09g = 5.9mol ` 12g/mol

H: 6.71g = 6.71mol 1g/mol

O: 11.84g = 0.74mol N: 11.84g = 0.74mol 16g/mol 14g/mol

2. Normalize-Divide by smallest value: C: 5.9mol = 8 0.74mol

H: 6.71mol = 9 0.74mol

3. Multiple by integers if necessary: C8H9ON X 1 = C8H9ON 4. Divide given MW by empirical MW: Given MW = 135.068g/mol = 1 Empirical MW 135 g/mol

O: 0.74mol = 1 0.74mol

N: 0.74mol = 1 0.74mol

IHD = (2n+2) – (X+Y) = [(2 X 8) – (9 – 1)] = 5 2 2 IR Spectroscopy Unknown Organic Liquid, P: Wavenumber (cm-1) 3328.04 2958.27 1113.31

Functional Group Alcohol (OH) Alkane (CH) Carbonyl (CO)

Table 2 Determination of functional groups through the wavenumbers of the peaks of the unknown organic liquid sample.

Unknown Organic Solid, O: Wavenumber (cm-1) 3060.87 1661.39 1552.83

Functional Group Aromatic Ring Carbonyl Nitrogen Bond (NO)

Table 3 Determination of functional groups through the wavenumbers of the peaks of the unknown organic solid sample.

Melting and Boiling Points Unknown Organic Liquid, P: Range: Started Boiling Vaporized Completely

Trial 1 (◦C) 107 115

Trial 2 (◦C) 108 111

Table 4 Boiling points of unknown organic liquid sample, P. Trial 1 had a non-precise boiling range of 107-115◦C, where it began to boil at 107◦C and completely vaporized at 115◦C through a drastic increase in temperature. However, at a gradual pace of increasing increments, Trial 2 had a more accurate boiling range of 108-111◦C where it began to bubble at 108◦C and vaporized completely at 111◦C.

Unknown Organic Solid, O: Range: Started Melting Liquefied Completely

Trial 1 (◦C) 117 120

Trial 2 (◦C) 115.4 118.9

Table 5 Melting points of unknown organic solid sample, O. Trial 1 had a non-precise melting range of 117-120◦C where it began to melt at 117◦C and at 120◦C, the sample was transformed into a liquid. However, in Trial 2, it was more accurate with a melting range of 115.4-118.9◦C. Trial 2 began to melt at 115.4◦C and at 118.9◦C, the sample melted completely.

Conclusion: The purpose behind this Lab 1 is to learn the techniques to identify unknown organic liquid and solid compounds. With the use of the four techniques-Molecular Formula, IHD, IR Spectrum, and MP/BP-to identify the unknowns, the unknowns were recognized for samples P and O. Table 6 concludes the experiment’s data. The Molecular Formula of sample P is C4H10O and its boiling point was ranged between 108-111◦C. Three peaks on the IR spectrum were discovered. The spectrum revealed an alcohol group, an alkane group, and a carbonyl group. With the help of the Merck Index and the Aldrich Catalogue, the unknown organic liquid sample, P was discovered to be one of two choices: a 2-Butanol compound, shown in Figure 2, or a Diethyl Ether compound. However, the unknown organic liquid sample is more closely related to 2-Butanol which has a boiling range of 98-100◦C, something sample P is nearly within the range of, a molecular formula of C4H10O, and a similar IR spectrum. The difference in ranges can be due to human error or a lack of steady temperature rate. The unknown organic solid liquid, O has a molecular formula of C8H9ON and has a melting point with a ranged between 115.4-118.9◦C. Its IR spectrum contains three distinctive peaks: an aromatic ring, a carbonyl group, and a nitrogen bond. With the help of the Merck Index and the Aldrich Catalogue, the unknown organic solid sample, O was discovered to be an Acetanilide, This could be seen in Figure 3. The Acetanilide compound, which has a melting point of 114.3◦C, something outside of sample O’s melting range. This could be due to a slower visual of the start of the melting, thus assuming human error, or this could be a too quick gradual increase in temperature increments, making it impossible to locate the exact time the solid began to melt.

Figure 2 The structure of 2-Butanol was concluded to be the unknown organic liquid sample, P.

Sampl

MF

IHD

MP

Figure 3 The structure of Acetanilide was concluded to be the unknown organic solid sample, O

BP

e O

C8H9ON

5

115.4118.9◦C

---

P

C4H10O

0

---

108-111◦C

IR Spec

OH CH CO Ring CO NO

Structure Elucidation Acetanilide

2-Butanol Diethyl Ether

Table 6 A summary table. The samples are the unknown organic solid (Sample O) and the unknown organic liquid (Sample P). The molecular formula (MF) of Sample O is C8H9ON, while the molecular formula (MF) of Sample P is C 4H10O. The Index of Hydrogen Deficiency (IHD) of Sample O is 5 while Sample P is 0. Sample O is a solid, so the melting point (MP) was discovered to be around 115.4-118.9◦C. Sample P is a liquid and was tested for its boiling point (BP) which was discovered to be between 108-111◦C. MP was not tested for Sample P and BP was not tested for Sample O. While preforming an Infrared Spectroscopy (IR Spec), three peaks where determined for each sample. Sample O was concluded to have an alcohol group (OH), an alkane group (CH) and a carbonyl group (CO). Sample P was concluded to have an aromatic ring, a carbonyl group (CO), and a nitrogen bond (NO). Through observation, it was determined that Sample O could be an Acetanilide compound and Sample P could be either a 2-Butanol compound, or a Diethyl Ether.

References: Gilbert, J.C., and Martib, S.M., Experimental Organic Chemistry: A Miniscale and Microscale Approach, 4th Edition, Cengage Learning, Boston, MA, 2006. Landrie, C.L., and McQuade, L.E., Organic Chemistry: Lab Manual and Course Materials, 5th Edition, Hayden-McNeil, LLC, Plymouth, MI, 2016....