Melting Point Determination of Salicylic Acid

Obtaining the Melting Point of a Known Compound

• Obtain 15 mg of salicylic acid, grind to a fine powder using a spatula, and transfer to a watch glass
• Obtain two melting point capillary tubes, one end closed and one end open
• Tap open ends of tubes in the powder for approximately 1 cm sample
• Connect melting point (MP) device to outlet
• Select manual method
• Set the instrument, ensuring the start temperature is 5°C below and end temperature is 5°C above the literature melting point
• Salicylic acid's melting point range is 158-160°C per the literature
• Press start>continue and wait for the instrument to indicate it is ready
• Check start temperature (on display) matches set value
• Insert first capillary (closed end down)
• Save other capillary for later use
• Press start and wait to complete the run
• Collect data once finished
• A range of MP (start and end) will be found
• Record value in data table-1
• Dispose of capillary into "broken glassware" labelled bucket
• Repeat steps 4-12 using a heating rate of 2°C/min instead of the previous rate for the second capillary tube of salicylic acid

Obtaining the Melting Point of a Mixture

• Weigh and add 10 mg of salicylic acid with 10 mg of acetaminophen, grind, mix well, and transfer into a watch glass
• Record in data table-2
• Repeat steps 4-12 with the mixed compound at heating rates of 4°C/min and 2°C/min
• Record in data table-2
• Set the start temperature 10°C below the lowest MP of the mixed samples, and end temperature a similar amount above the highest MP of the mixed samples
• If mixing salicylic acid and acetaminophen, set start temperature at 148°C (10°C below salicylic acid) and end temperature at 170°C (MP of acetaminophen)

Identifying an Unknown Compound

• Obtain an unknown sample from the instructor and note the sample in the lab notebook
• Repeat steps 4-12 using heating rates of 4°C/min and 2°C/min
• Record in data table-3 -Select a start and end temperature range that covers all possible samples, as the identity of the unknown is not known
• After the first run at 4°C/min, a range for the unknown will be known
• Set start and end temperatures within ±5°C of this range the second time at 2°C/min to minimize the experimental time
• Possible unknown options include: -Salicylic acid -Acetylsalicylic acid -Acetaminophen
• Find the name of the unknown and report it
• Unplug all electronic devices

Clean Up

• All solid waste goes into the regular trash
• MP tubes go into the glass waste bucket
• Clean the bench before leaving
• Check the blackboard for post lab questions

Experiment #2: Extraction of Benzoic Acid

• Extraction is a standard method for isolating a pure product by removing undesired byproducts, unreacted starting material(s), and the catalyst, often referred to as washing.
• Extraction removes target compound from an impure matrix
• Washing removes impurities from the target compound such as removing water via extraction with saturated sodium chloride solution or removing mother liquor adhering to the crystal surface during recrystallization.

Basics of Extractions

• Extraction transfers compound(s) from a solid or liquid into a different solvent or phase
• Examples include extracting tea flavor from tea bags with hot water, decaffeinating coffee with solvents/CO2, and using vanilla extract from plant materials using alcohol
• Liquid-liquid extraction is common in chemistry labs, often using a separatory funnel with an aqueous and an immiscible organic solvent that are shaken together
• Components move from one layer to the other

Key Principles

• Compounds move from one liquid to another based on relative solubility
• "Like dissolves like" meaning nonpolar compounds extract into nonpolar solvents, and vice versa
• Polar compounds such as those responsible for the taste and color of tea, readily extract into hot water
• Most compounds end up in the layer they are most soluble in, when the mixture is allowed to equilibrate between two liquids

Acid-Base Chemistry in Extractions

• Many liquid-liquid extractions use acid-base chemistry where liquids must be immiscible to form 2 layers

• Most extractions use aqueous solutions

• Must consider miscibility of solvent with water and compatibility of the reagent with the mixed compounds/solvent to be extracted

• Solvents like dichloromethane, chloroform, diethyl ether, or ethyl ester form two layers with aqueous solutions if used in sufficient quantities

• Ethanol, methanol, tetrahydrofuran (THF) and acetone are not suitable due to complete miscibility with most aqueous solutions

Solvents

• Phase separation can be achieved by "salting out" or adding large amounts of salt
• Commonly used solvents: -Ethyl acetate (8.1% dissolves in water) -Diethyl ether (6.9% dissolves in water) -Dichloromethane (1.3% dissolves in water) -Chloroform (0.8% dissolves in water) -All dissolve up to 10% in water
• Water also dissolves in organic solvents like: -Ethyl acetate (3 %) -Diethyl ether (1.4 %) -Dichloromethane (0.25 %) -Chloroform (0.056 %)
• Oxygen containing solvents are generally more water soluble due to their ability to act as hydrogen bond donors and acceptors
• Increased water solubility lowers the solubility of weakly polar or non-polar compounds in these solvents such as wet Jacobsen ligand in ethyl acetate
• Other solvents like alcohols increase water solubility in organic layers because they are miscible with both phases and act as mediators which leads to emulsions

Understanding the Extraction Process

• Determining which layer contains the product is most important
• Most organic compounds dissolve better in the organic layer than aqueous solutions unless converted to an ionic species to be more water-soluble, such as carboxylic acids or amines
• Chlorinated solvents like dichloromethane and chloroform are denser than water, while ethers, hydrocarbons, and esters are less dense than water
• One should never dispose of any layer until absolutely (=100 %) sure that the layer is not needed again, with confirmation after isolating the final product in a reasonable yield and been identified as the correct compound
• Product recovery is easier out of a separate layer than removal from the waste container
• Properly label all layers

Chemically Modifying Compounds

• Compounds are often chemically modified to make them more ionic by adding a base to convert a carboxylic acid to a carboxylate
• Standard solutions include 5% hydrochloric acid, 5% sodium hydroxide solution, saturated sodium bicarbonate solution (~6 %), and water to modify the organic compound
• Makes it more water-soluble and removes it from the organic layer
• Concentrated solutions not regularly used due to increased heat evolution and potential side reactions

Reagents

• Benzoic acid, with a melting point of 122 °C
• Sodium bicarbonate
• Dichloromethane (DCM), with a density of 1.33 g/mL
• Sodium Chloride
• Calcium chloride

Extraction Procedure of Benzoic Acid

• Two tests tubes are labeled 1 and 2

• 0.18g of impure benzoic acid, 2.0 mL of dichloromethane (DCM), and 2 mL of saturated sodium bicarbonate solutions (NaHCO3) is added, capped, and well mixed to test tube 1

• Two layers form: top layer is aqueous (NaHCO3) layer and bottom layer is organic (DCM) layer because DCM has a higher density than water

• Benzoic acid product will be in the aqueous layer (top) after the reaction

• The top aqueous layer is pipetted out into test tube 2 using with a glass pipette with a bulb. The pipette should be kept for future use

• 0.5 mL (7-8 drops) of NaHCO3 is added to test tube 1, capped, and well mixed. Two layers form as earlier

• The top aqueous layer is pipette out to test tube 2

• Another 0.5 mL (7-8 drops) of NaHCO3 is added to test tube 1, capped, and well mixed. Two layers form as earlier

• The top aqueous layer is pipette out to test tube 2

• Once test tube 2 is evaluated, it should only consists of one aqueous layer

• Should any organic (DCM) layer remain in the test tube, it must be removed back to Test tube 1

• Conc. HCl is added to test tube 2 drop by drop to make the solution acidic and observe a white precipitate form (PPT)

• A maximum of 0.9 mL or 14 drops of conc. HCl should be added before the test tube is placed in in an ice bath for 5 min

• The PPT is filtered using vacuum filtration and rinsing the test tube with cold DI water while the precipitate is transfered to the filter funnel with a spatula

• The PPT should be spread out to dry on the filter funnel for at least 5 min using the vacuum suction and spatula. The drying process should be expediated by breaking the large chunks and mixing with a spatula

Extraction Procedure Continued

• The recovered product should be weighted for the record of acutal yield
• The product should be evaluated for % recovery calculation
• The purity of the product must be checked by MP test

Obtaining Melting point

• One melting point capillary tube must be obtained (one end closed, one end open)
• Make sure to add 1 cm worth of product into the capillary tube
• The open ends must be tapped on the vacuumed product to add a small amount
• The MP device is connected before the first capillary is placed (closed end down) into one of the whole of the melting point apparatus. Allow rest of the holes for other groups
• The manual method must be selected and tuned according to the picture-right
• The test is started with start>continue>start, and you must wait for collection of data to finish
• A range of MP would result and compared how much closer it is to the literature MP

Expected MP conclusion

• Benzoic acid should have a MP of 122 °C
• Experimentally, a experimetnal range should results in a 118-120.6 °C range
• If the expereimental range is not within 2 °C of the literature range than the product is not considered pure
• The conclusion should discuss the purity bsaed on the conducted experiemnt

MP Analysis

• Discuss purity in conclusion -MP analysis is expected to lead to a similar melting point

Waste management

• Capillary should be disposed into a "broken glassware"
• All excess benoic acid should be trashed regularly
• Aqueous layer disposed to the sink
• Solid sticks trashed after wash with acetone
• All bulb returns to origin

Microscale Laboratory Techniques

• Extraction glasswear item used is a extraction

Experiment: Thin Layer Chromatography (TLC)

PURPOSE -Select a solvent system to separate a mixture of biphenyl, benzhydrol, and benzophenone using chromatography (TLC). -Identify each compound's retention factor (Rf). -Investigate solvent polarity effects on relative mobilities of compounds in a mixture, and use TLC to identify specific compounds present in an unknown mixture containing any combination of biphenyl, benzhydrol, and benzophenone.

TLC Basics

• TLC is an indispensable tool which quickly and efficiently separates small quantities of materials
• Applications of TLC include: -Rapid analysis of reagent and/or product purity -Quickly determine the number of compounds in a mixture
• Comparing behavior to knowns allows tentative identification

TLC Applications

• Progress of a reaction can be followed by monitoring disappearance of a reactant
• TLC helps select a TLC solvent

Understanding Chromatography Techniques

• Chromatography includes TLC and includes a two phase operation which is all techniques used during the process -Mobile phase (either a liquid or a gas) is the first medium -Stationary phase (solid support) is the second medium and contains an adsorbent or liquid
• Samples move through stationary phase due to attractions to either mobile or stationary phase
• "Like dissolves like" can be applied to predict attraction -Polar attracts polar -Non-polar attracts non-polar
• Individual compounds separate based on differing attractions
• Depending on method can either be detected or collected, but in TLC, the individual compounds are detected

TLC Specifics

• Capillary action allows mobile phase to ascend stationary phase via a plate
• Sample mixture is applied near the bottom of the plate which is then placed in a developing chamber
• As mobile phase ascends, mixture compounds dissolve due to solubility in the mobile phase versus the stationary phase

Key features

-Solid stationary phase adsorbent adsorbs mixture compounds

• Eluent front, (line of the mobile phase) travel over adsorbent, compound mixes move at different rates -Compounds with less attraction more further with eluent
• Compounds with more attraction move slowly
• The more polara compound adheres to adsorbent

The Retention Factor (Rf)

• The ratio of the distance the compound moves to the distance of the eluent front move
• Rf = distance traveled by the compound/distance traveled by eluent
• Chromatographic behavior is long as it is reproducible if the following are kept consent in the equation- -Stationary phase, mobile phase, temperature,

TLC Materials

• Common adsorbent is silica gel (SiO2 x H2O)
• Eluents are organic compounds of varying structure and polarity
• Eluents can be combined to fine-tune polarity for maximum separation
• Eluent selection involves trial and error

TLC Equipment

• TLC chamber (100 mL beaker)
• TLC Spotter
• TLC plate
• Ruler
• Pencil -Watch glass
• Plastic pipette or glass pipette
• Small Erlenmeyer flask or test tube

TLC Reagents and Properties

Safety

• Required PPE: goggles, gloves (recommended)
• Solvents used are: flammable, irritating, and/or toxic, use a these in fume hood
• Sample compounds are :flammable and irritating, use in a fume hood
• UV lamp is dangerous, do not look directly into it

TLC Procedure: Plate Preparation

• Use a 100 mL beaker (neat, clean and dry) with watch glass to create a developing chamber
• Three TLC plate, spotter, scale ruler is requreds to avoid contamination
• Unknown is taken and number is noted for comparison, mark origin and identify with working eluent examples
• 3 Small samples needed- take 10-25 mL flask and test tube, use gloves to avoid contamination

TLC: Plate Spotting

• Each flask is labelled samples 1. Benozphenone 2. Biphenyl 3. Benzoin
• 5 mg needs to be allocated to the solution, 1 Ml of the solution is then tested for stock
• Stock soultion then prepped with the TLC spotter (make sure to avoid contamination)
• The spotter is put solution stock - the solution then transferred aonto plate (avoid contamination), then UV light is emitted for the results

Developing and Evaluating TLC Plates

• Take the developing chamber (100 mL beaker) and watch glass which were prepared earlier
• Fill it with the solvent Tips: 1:1 equivalent means similar amount equivalent of EA and Hexane -Use the correct number TLC- TLC Chamber, TLC Plate, Mobile phase level
• 1:1 ration must be the standard test and each test must be checked with a UV light
• The chamber musnt be contaminated or the test is void
• Test results are compared to the standard solution chart

TLC: Analyzing an Unknown Mixture

• Obtain a new TLC plate and spotter, and prep plates
• Unknown smaple (step 14) solution should be conducted and results compared to the standard chart.

Cleaning for TLC

• Use trash, wash and never toss solvent glass

Key chemicals

• Hexane and Acetyl

N.B

To fully complete: need to bring all results to the instructor for grading after

Recrystallization procedure

Understanding the Solvent screening table-

• • S = soluble, PS = partially soluble, I = insoluble
• • LT = Low temperature, RT = Room Temperature, HT = High Temperature

Procedure checklist

1. Prep - Take four test tubes, rinse, then test the 1 ml of the acetone in with paper towels and solvent disposal
2. Four labelled tubes
3. ice baths created
4. 50mg tests allocated to each ice bath
5. label solvents allocated to each (1 ml of solution )
6. Wait for 1 min of ice bath and document
7. Solvents prepared ( test table created S, PS, I and label)
8. Water mixture is heated 90-100 (warm (but no boil))
9. Solution added until it becomes diluted and clear

Recrystal process

14. 250mg sample is obtained
15. ml solvent fresh is aded ti the flask (document results on the table)
16. The water bat tested (avoid burn) 17.. Pipette used to add solvent results drop by drop by 5

• The liquid it test to clear

18. After results occur , 5 min is waited in order to dry material
19. Ice path process prepped

• Clean spatula and scrape

20. Vacuum filtration is the next

• Cold water used 21.. Crystral wait for 5 min

22. Weight and record
23. % is created / recorded 24 . If you do not see any crystal - follow the label

• Parafilm
• Instructor must save
• Test must be documented in the lab

Final Analysis by MP:

• Must prepare product before the test
• End closed process must be followed (capalaries)
• Pre made heat settings are prepared-

Main test points

3. MP MUST BE 114
4. Extarctions need to follow doc
5. Must evaluate MP (expermental vs test/report)

Main safety

• Trash
• Solvents (in hood) needs to be clean
• If trash do not dump

Key notes from "Experiment" Section: Separation by Distillation

• Distillation separates compounds via boiling point as compounds are boiled, the vapors are re-liquified via the condenser, and collected in a receiver
• Distillation has numerous methods:remove volatile from non-volatile, separate volatile, separate more volitiale

Miscibility with Liquids And Temperature

• Miscible are liquid mixes, which are bolied at a temperature that effects the boiling compound.
• Ethanol and water are examples, 78 degrees vs 100 means the soultion will measure 90°C degrees

Key Materials

• Distate is formed from the condensation, and moves into the condenser.
• Distialte contains 84g or more the compound that causes boiling
• If one compound is highly volitale over the other, then vaporization occurs.

Distillation Types

1. Simple - Flask bottom RBF
2. Distillation orfractiontalized -. column that fractionlized placed

• Vapor in RBF must contact cooler so the condense occures and reheats the liquid
• Condensed liquids that are hot will reheate and re vapourize.

Key Information for Fractionalizing

• In the flask: -At same time, , vapor cools and enriched while the condensed fall that are less volatile, which helps with extraction method

Key Info and parts on the distillation process

-Theoreitcal is formed (by each Condensation) fractionating column : high levels and degrees over mixtures

• The columb must remain verticle
• Vapor colum is importnat factor for best preform (the rate is key)

How to Monitor Process

• Condensation line shows vapor

• Heat can be monitored via thermometer, higher the heat - more results via disilation • Fractionating column used, or the column is inefficient
• Temperature should be monitored, 105 is too high, but 70 is the lowest

Materiails in distillation Equipment Section

• 150°C - themonitor
• Flask RBF 5ml
• heat plate + monitor adapter
• chip small

Regants:

Toulene (Weight MW) 86.18 (Weight MW) 0.672 g (Weight) 68-70 °C

Safety to the distillation Section

• The following gear required"
• goggles
• gloves
• apron "Follow precautions due to heat and air levels with equipment, as material is hazardous!

Distillation proccedures Section "key points"

• The appraturs must be clean and set before the heat
• Use a distillation
• Collect any info from other workers

Manual Distillation section.

• The apparatus must be stable and insulated pre experiment
• The solutions needs to: - 2 ml toelune -2ml hexzane
• Need to add in the chip due to the high rate of combustability
• Heat cant touch the flask and must flow to see results

Precautions for Safety

• Heat must be 150°C - slowly rasing on tests
• Spoon can be used to protect hands and surface
• 2. Thermo reader is key
• Then follow, until 3ML or 1L has passed
• Test results needs recorded + compared

Fractional results section:

• The similar distillation tests occurs as in the earlier procces*
• But must have different set ups and levels of the heat and equipment (follow guidelines).

Clean Up:

• Follow hazardous guides
• Chips thar arent good must be trashed
• Acetone is trashed and glass water
• Then equipment is saved

Data Section:

Drop amount

• Then degrees Create a colum in graph

Learn how to determine the melting point of salicylic acid using a melting point apparatus. The process involves preparing the sample, setting up the instrument, and recording the melting point range. Proper technique ensures accurate results and safe disposal of materials.