Green Oxidation of Borneol to Camphor using Oxone PDF

Preview

Summary

Lab Report ...

Description

Green Oxidation of Borneol to Camphor with Oxone Mercedes Erpelding TA Maetzin Cruz Chemistry 2311 Section 4 November 6, 2017 Purpose: The experiment demonstrated the oxidation of (1s)-borneol to camphor. Camphor is naturally synthesized in nature and is used in many medical applications. Recently, oxone has been used as an oxidizing agent which offers a safe alternative to the commonly used chromium reagents. The by products of chromium salt from the oxidation of chromic acid have been known to be harmful to the environment and humans. The resolution to this problem is the replacement of chromic acid with oxone and NaCl, which are more favorable to the environment and humans. The experiment was a small scale oxidation and the product produced was extracted, desiccated and sublimed. H NMR, melting point and IR spectroscopy was used to analyze the purity and corrected yield of the final synthesized product. Scheme:

Figure 1. Green Oxidation of (1S)-Borneol to (1S)-Camphor with Oxone Scheme

Mechanism: The green agent used in the experiment, oxone, oxidizes the chloride ion from the

NaCl into a molecular chloride. The molecular chloride interacts with water and forms a protonated HOCl. Chloride is released from HOCl to become a chloride ion by gaining an electron and adds to the OH on the 1(s)-borneol. The oxygen from the water deprotonates the carbon that has the O attached to it, which loses an electron to be reduced.

Figure 2. Green Oxidation of (1S)-Borneol to (1S)-Camphor with Oxone Mechanism

Procedure: The procedure followed was on pages 131-136 of the Wissinger Manual. Modifications to the procedure included adding 1.5 mL DI water 5 minutes after NaCl was added during the first stirring step of 50 minutes. Additionally, the sublimation technique was performed before desiccation and was altered by using a 150 mL beaker with a 100 mL round bottom flask containing cold water and placed on top of the beaker and secured with parafilm. Furthermore, in addition to the H NMR discussed the procedure, a IR was performed and the melting point was analyzed for the final sublimed product.

Starting Reagents and Product Table 1 (1S)-Borneol

Oxone Triple Salt

Active oxidizing Agent KHSO5 (Calculated)

NaCl

(1S)-Camphor

Mol. Wt

154.253

307.380

152.178

58.4430

152.237

grams

1.131

2.541

2.541

.0930

mmols

7.332

8.267

16.70

1.591

Melting pt (celsius)

202

255-263

255-263

801

175-177

Density g/mL 1.01

1.12

1.12

2.17

.992

Solubility

Slightly Soluble in water

Soluble in water

Soluble in water

Soluble in water

Soluble in organic

Hazards

Flammable

Oxidant and Corrosive

Oxidant and Corrosive

Irritant

Flammable

● Oxone as KHSO5*½ KHSO4*½ K2SO4 www.Pubchem.com Results and Observations: Before the addition of deionized water and the 50 minute oxidation, the mixture was a cloudy, milky color. As the oxidation reaction took place, the mixture turned clear. When the additional .03 grams of NaCl was added, the reaction mixture turned a yellowish color. In the reaction round bottom flask there appeared to be 2 layers formed. It can be predicted that the bottom layer was aqueous NaCl and oxone solution, while the top layer was organic that still had starting materials due to the associated densities of each. When a drop of the aqueous layer was dipped onto a starch-iodine paper, it turned brown due to the presence of oxidant, therefore, excess sodium bisulfite was added until no color change was seen on the starch-iodine paper. During the extraction, organic solvent ethyl acetate was used and the more that was used, the more the organic top layers volume increased. The aqueous layer was a cloudy mixture while the upper organic layer was clear. NaCl (brine) was also used for extraction in order to further separate the organic and aqueous layers. The magnesium sulfate was used as a drying agent and was added until no clumping was seen. After gravity filtration, the liquid was very clear. When the filtered solution was heated to remove remaining ethyl acetate in the mixture, the mixture became solid and turned a white color. The heating process took about 10 minutes and yielded . 256 grams crude (1s)-camphor. After the extraction was complete, .150 grams crude (1s)-

camphor was weighed for sublimation and desiccation. The sublimation caused white crystal product to be observed on the bottom of a round bottom flask and the inner walls of the beaker of the sublimation apparatus. The amount of product recovered from sublimation was .073 grams. The .073 grams of the sublimed product was then used for desiccation process. The desiccation chamber contained calcium chloride and was contained in the lab drawer for about 44 hours. After desiccation, .051 grams remained of (1s)-camphor. Of the .051 grams of sublimed/dessicated (1s)-camphor, .021 grams was used for H NMR spectrum analysis and .018 grams was used for IR spectroscopy. The remaining .012 grams was used to analyze the melting point of the final product. The product was observed to start melting at 175.6 degrees celsius and was melted completely at 177.2 degrees celsius. The literature melting point range for (1s)camphor is 175-177 degrees celsius. Yield of Crude Product Table 2 Theoretical Actual Yield grams Yield grams

% Yield

Correct yield grams

Corrected yield %

Literature Melting Point (Celsius)

Melting Point Celsius

1.07

23.93

.219

20.5

175-177

175.6-177.2

.256

Yield Sublimed of (1S)-Camphor Table 3 Mass before Sublimation (grams)

Mass after Sublimation (grams)

Yield % Sublimation

Corrected Yield (grams)

Corrected Yield %

.150

.073

48.7

.062

41.3

Yield of Desiccated of (1S)-Camphor Table 4 Mass before Desiccation (Grams)

Mass after Desiccation (Grams)

Yield % Desiccation

Corrected Yield (grams)

Corrected Yield %

.073

.051

69.9

.044

60.3

Purity of (1S)-Camphor Table 5

Integration area of single H from starting material (Hd’)

Integration area of single H from product (Hd)

Mole Grams Ratio Borneol Camphor to Borneol

Grams Camphor

% Purity (1S) Borneol

% Purity (1S) Camphor

.1 cm

.6cm

.6/.1

91.342

14.45

85.55

15.425

IR Spectrum of (1S)-Camphor (Neat) Table 6 Type of Bond

Observed Frequency (cm-1)

Intensity

Alkane C-H bending (CH3)

1372.3, 1390.6

Weak

Alkane C-H bending (CH2)

1416.4, 1451.7

Weak

Ketone C=O stretch (unconjugated)

2876.1, 2961.0

Moderate-Strong

Ketone C=O Stretch (unconjugated)

1739.7

Strong

Ketone C=O stretch overtone

3466.1

Weak

*C-Cl stretch

703.7, 738.8

Moderate-Strong

*H-C-H out of plane wagging

1021.4,1047.3

Weak

*C-C stretch

1266.0

Moderate

*Asymmetric Alkane C-H Stretch

3055.1

Weak

* Peak is from the methylene chloride

H NMR Spectrum of (1S)-Camphor (300 MHz CDCl3) Table 7

Protons, Hx

Chemica l Shift, ppm

Splitting Patterns

J Values, Hz

Integration , cm

Calculated #H’s

Actual # H’s

Ha

.840

Singlet

N/A

4.0

7

3

Hb

.909

Singlet

N/A

2.8

5

3

Hc

.948

Singlet

N/A

2.7

5

3

Hd

1.324

Multiplet

9.6

.6

1

1

He

1.418

Multiplet

5.1

1.1

2

1

Hf

1.669

Multiplet

9.3

1.1

2

1

Hg

1.834

Doublet of Doublet

18

.8

1

1

Hh

1.925

Multiplet

4.2

.9

1

1

Hi

2.079

Multiplet

4.5

.8

1

1

Hj

2.344

Doublet of Doublet

10.5

.8

1

1

(1s) Borneol Hd’

1.233

Multiplet

N/A

.1

1

1

Conclusion and Discussion: The result of the experiment was the synthesis of (1s)-camphor by oxidizing the starting material (1s)-borneol. Purification of the crude product was achieved by extraction, sublimation and desiccation. The % yield after purification was 20.5% with a purity of 85.5% determined by the H NMR using integration values for both (1s)-camphor and (1s)borneol. The yield calculation inferred that the purity would be the same for both the desiccated and sublimed products. In actuality, the purity for the desiccated product was predicted to be lower and would have lowered the product yield even further. In other words, a better approach to a more correct yield would have included desiccation of all .256 grams of the crude product before sublimation. In addition, the product yield could have been improved by minimizing product loss by increasing the reaction time and by adding the products with more precision. The Sublimation performed took advantage of camphors very low vapor pressure (.65 mmHg at 25 degrees celsius) occurring below melting.2 Camphor was able to phase shift from solid to gas directly with a slight amount of heat. It is expected that sublimation is a effective way of purifying the (1s)-camphor from the starting material (1s)-borneol because (1s)-camphor has a lower vapor pressure than (1s)-borneol (33.5 mmHg at 25 degrees celsius).2 The lower vapor pressure of (1s)-camphor allows it to be more likely to vaporize onto the bottom of the

round bottom flask in contrast to the larger vapor pressure of (1s)-borneol which is less likely to vaporize. Despite the likeliness of (1s)-camphor to vaporize before (1s)-borneol, the H NMR indicated that there was still (1s)-borneol present in the sublimed product. The small presence of (1s)-borneol could have been due to the scraping off solid from the sides of the beaker. Residual water could have been left over in the final product after sublimation but should have been removed after desiccation. In the IR spectrum, there was no observed frequency for the O-H stretch of the starting material (1s)-borneol but there was frequency observed for the ketone C=O stretch including the overtone stretch, which shows that (1s)-camphor was synthesized. Additionally, the position of the C-H bonds in (1s)-camphor effect the presence of the C-H alkane stretch frequency which shows up as two peaks on the spectrum. Finally, methylene chloride, which was used as the solvent to dissolve the solid (1s)-camphor on the sodium plates was also observed on the IR spectrum. The H NMR spectrum in addition to the IR spectrum also supported the synthesis of (1s)camphor. The H NMR also showed minimal traces of (1s)-borneol present after both sublimation and desiccation. The mole ratio of (1s)-camphor to (1s)-borneol from the H NMR spectrum was determined to be .6/.1 or 6/1. If sublimation would have been performed more properly, the mole ratio would show more camphor to borneol or more camphor to no borneol. In addition to the observations from the H NMR, the products melting point range was observed at 175.6-177.2, with 177.2 being the temperature that the product completely melted. The observed melting point range is within the range of the literature melting point of (1s)-camphor but also .2 degrees celsius above the literature melting point. The observation of the higher melting point could be affected by the small presence of borneol in the product which has a melting point of 202 degrees celsius. Observations from the IR spectrum, H NMR Spectrum and melting point supported the conclusion that the synthesis of (1s)-camphor was achieved and the reaction was successful. Although, the final product did contain small traces of the starting material, (1s)-borneol, but in such minimal amounts, it wasn’t detected by IR spectroscopy. In conclusion, the experiment used three green chemistry principles which made it an overall success. The first green chemistry principle used was the use of environmentally benign waste. This experiment successfully produced only environmentally benign waste by only producing excess salt in the aqueous solution, which in the end of lab was neutralized and washed with water down the drain. The second green chemistry principle present in the experiment was the use of safer reagents. The oxidizing reagent used in the experiment, oxone, is more environmentally safe in comparison to the traditionally used,chromium, which is harmful for both humans and the environment. The third green principle followed through the experiment was the use of renewable feedstocks. The starting material (1s)-borneol is a renewable feedstock because it is naturally occurring and i can be synthesized by reduction of camphor in the reverse reaction. Oppositely, a green chemistry principle which is not present in the synthesis of camphor is catalysis. The sodium chloride was used as a catalyst in the experiment while the oxone was used as the oxidizing agent and was consumed. This could be positively changed by involving a reaction at the end to restore the active state of the oxone.

References:

1. Wissinger, J.E. A Green Chemistry Approach Laboratory Manual. Hayden-McNeil, LLC: Plymouth, MI, 2018, pp, 131-136. 2.

https://pubchem.ncbi.nlm.nih.gov...