CHEM 234 Reaction Schemes Questions The reactions to be drawn on chem draw with names of reactants products and reagents with all the reaction conditions a

CHEM 234 Reaction Schemes Questions The reactions to be drawn on chem draw with names of reactants products and reagents with all the reaction conditions and answer the questions attached.

Analine: 2-aminobenzensulfonic acid

Coupling Agent: 2-napthol and 8-anilo-1-napthalensulfonic acid, ammonium salt.

Also is it possible to send the answers to me by email instead of attaching to the chat? Experiment 5
Conjugation and Color:
Synthesis of Azo Dyes
Objectives
1.
2.
3.
As an example of combinatorial chemistry,
you will perform the chemical synthesis of
two (2) azo dyes, an important class of color
producing compounds.
Discuss the correlation between chemical
structures and color observed, an example of
structure-activity relationship (SAR).
You will perform the dyeing (coloring) of
different fabrics. Then, analyze the
relationship between color retention and
chemical structure of each fabric.
Preparation
Organic text: Review the formation, reactions and
properties of diazonium salts.
Notebook: Complete the notebook with the rubric
provided. Obtain information for the chemicals
involved in this experiment. All calculations
involved must be clearly written.
You will be synthesizing dyes. Without proper
care, you risk staining your notebook and/or
clothing.
Safety: Pants, shoes, socks, goggles and a lab coat
are required for the experiment.
Work safely in your fume hood, and avoid spilling
chemicals on your lab notebook.
Grading: You are required to have your TA
inspect your dye product before disposal. The
completed multifiber fabric patch should be
thoroughly dried and turned into your TA, along
with the identities of your starting materials.
Reading Assignment
Combinatorial chemistry is the simultaneous synthesis of large
numbers of compounds that are systematic variants (analogs) of
a chemical structure. A group of analogs produced by such a
method is known as a library. The main objective of
combinatorial chemistry is to discover a compound within the
synthesized library for pharmacological, materials, or chemical
purposes.
This approach contrasts a traditional organic synthesis where
molecules are engineered, one by one, to fulfill (study) a given
function. Pharmaceutical companies have large collections of
compounds synthesized by the traditional synthetic methods,
which have already been screened heavily for physiological
activity. Much time and effort has been invested in them.
Azo Dyes
Most azo dyes can be prepared by combining a diazonium salt
(diazo component) with an activated aromatic compound
(coupling component). The preparation of the dye involves
two stages: (1) diazotization and (2) coupling.
In the (1) diazotization stage, a primary aromatic amine reacts
with nitrous acid (HONO) to form the diazonium salt. Nitrous
acid is generated in situ from sodium nitrite and a mineral
acid (HCl). The reaction is carried out at a low temperature
because diazonium salts react with water to form phenols and
other by-products at higher temperatures.
Small biotech companies, who operate without the benefit of
large compound databases, were born concurrently with the rise
of combinatorial chemistry. Bringing a new drug to market
requires an investment of 12 to 15 years and as much as $500
million dollars. Using combinatorial techniques, thousands of
new compounds can be screened in days and new candidate
drugs can be developed in months. The success of these
techniques in the pharmaceutical industry have led to the
introduction of combinatorial chemistry into materials and
polymer sciences as well other consumer industries.
Parallel synthesis is an example of combinatorial chemistry.
There are many variations of this method but all rely on the
same general theme. A reaction vessel is prepared with an array
of individual wells. Along different rows or columns are applied
a given set of reaction components, resulting in a different
combination of components in each of the wells. The reaction
conditions to prepare each combination are identical.
Consider the following reaction:
A + B → A-B + C
We see that with this parallel method, four variants of A and
four variants of B can be combined quickly into 16
combinations. This is performed using a 4 x 4 grid of 16
reaction wells. Along each row is a single variant of A and
along each column a single variant of B. This type of synthesis
will be exemplified in the current experiment.
Deconvolution
Once a given library of compounds is created, members of the
library are tested for the desired activity. The process of
correlating the structure of a created compound to a biological
effect is known as deconvolution. In the current experiment the
desired biological activity is a particular color which you will
deduce as a class.
In the (2) coupling stage, the diazonium salt is added to a
solution of the coupling component, which is usually a phenol
or an aromatic amine. Phenols couple most readily in mildly
alkaline solutions, whereas amines react best in acidic
solutions. However, too low a pH will prevent an amine from
reacting by causing protonation of the amino group, whereas
too high a pH will cause the diazonium salt to change to a
diazotate ion, which is incapable of coupling.
Part (2) Coupling Reaction
Cl
NH2
Ph N N
Experiment 5
This week, you will synthesize two azo dyes assigned at the
beginning of the lab (combinatorial chemistry). Using the dyes,
you will color two pieces of fabric and post them for the rest of
the lab to see. Based on your experimental results and those
from other students, you will compare trends between structure
and color (SAR).
Ph
B
N
N
H
NH2
N
Ph N
NH2
Azo Dyes
The coupling reaction is an electrophilic aromatic substitution
reaction, with the diazonium salt acting as the electrophile. Because the diazo group is only weakly electrophilic, the coupling
component must contain strongly activating (electron-donating)
groups, such as -OH or –NR2, in order for coupling to occur.
Because of electron delocalization, the presence of auxochromes
affects (extends) conjugation and increases the wavelength
absorbed by the chromophore. Substituents at the 2,4 (ortho,
para) positions (with respect to the -N=N- group) in the aromatic
ring display a greater effect because they affect the entire
conjugated system.
Preparation
Cloth dyeing can be performed using many different processes.
In (1) direct process coloring, the dye is dissolved in water, the
solution is heated, and the cloth is immersed in the hot solution.
The dye molecules attach themselves to the cloth fibers by direct
chemical interactions.
In (2) disperse process dyeing, a water insoluble dye is suspended in water and a small amount of a carrier substance is
added. The carrier dissolves the dye and carries it into the fibers.
Using (3) ingrain process, a dye is synthesized into the fibers
themselves. The cloth is immersed in a solution of one of the
coupling components (for the synthesis of the dye), allowed to
dry, and then immersed in a solution of the second coupling reagent to develop the color. The small molecules may easily diffuse into the fabric and assemble to provide the desired color.
I.
Diazotization (formation of diazonium salt) is performed
using the following anilines (aromatic amines):
a.
b.
c.
d.
4-aminobenzenesulfonic acid
3-aminobenzenesulfonic acid
2-aminobenzenesulfonic acid
4-nitroaniline
II. Coupling (synthesis of azo dyes) is performed using the
diazonium salt from I, and two of the following coupling
reagents:
1.
2.
3.
4.
1-naphthol
2-naphthol
salicylic acid
8-anilinio-1-naphthalenesulfonic acid, ammonium salt•H2O
In this experiment, you will use direct process coloring.
Color perceived by the human eye arises from the wavelengths
not absorbed (reflected). In this experiment, most dyes will display shades of yellow, orange, red or purple (blue + red). While
yellow is associated with absorption of light of relatively short
wavelengths, red color is associated with absorption of longer A.
The light-absorbing portion of a dye (called chromophore) is a
highly conjugated system of delocalized n electrons. In Para Red
(the dye used to color the red stripes of the American Flag), an
extended conjugated system is clearly observed: a nitrosubstituted phenyl (benzene) ring is connected to a phenolsubstituted naphthalene ring through two doubly-bonded nitrogens. In general, the more extended the conjugation of the
chromophore, the longer the wavelength absorbed.
NO2
N
N
OH
Para Red
Certain substituents (on aromatic rings) can extend the conjugated
system by resonance (electron delocalization). These groups are
called auxochromes. Examples include the hydroxyl group (-OH),
alkoxy groups (such as -OCH3), amino groups (-NH2), (-NR2). The
common feature of these auxochromes is the presence of nonbonding electrons that can be delocalized into the highly
conjugated n system of the chromophore.
Carefully identify which dyes you have been assigned.
Diazotization of aminobenzenesulfonic acids a, b and c is
performed using procedure A. Diazotization of 4-nitroaniline (d)
is performed using procedure B.
Experimental Procedures
Procedure A. Coupling using the Diazonium Salt from
Aminobenzenesulfonic acids (a), (b), and (c).
Procedure B. Coupling using the Diazonium Salt from
4- Nitroaniline (d).
Part (1) Diazonium Salt Preparation
q In a test tube, place 0.49 g (2.8 mmol) of your assigned
aminobenzenesulfonic acid, 0.13 g of sodium carbonate, and
5 mL of water.
q Warming the test tube in a hot water bath to obtain a clear
solution.
q Remove the test tube from the water bath and add a solution
of 0.2 g of sodium nitrite in 0.5 mL of water (this is best
done in your 3 mL V-vial).
q In a second test tube, place 0.5 mL of concentrated HCl and
3 mL of ice-water.
q Place both test tubes into an ice-bath in a beaker until cold.
q Add the solution from the first test tube to the second test
tube dropwise with a Pasteur pipette. Swirl as the addition
progresses.
q Shortly after the addition is complete you should see the
precipitation of the diazonium salts.
q The suspension is used in the next step.
Part (1) Diazonium Salt Preparation
q In a medium test tube (tt1), place 1.5 mL of concentrated
hydrochloric acid and 1.5 mL of water. Place the test tube
(tt1) into an ice-water bath.
q In another medium test tube (tt2), place 0.7 g (5 mmol) of
4-nitroaniline, 0.38 g (5.5 mmol) of sodium nitrite, and
1.5 mL of water and mix the content well by using your
stir rod.
q Add the suspension in (tt2) to the HCl solution in (tt1) at
0 °C using a short-stem pipette. Stir the reaction mixture
during the addition with a glass rod and occasionally
there- after for about 10 min. Remove any solid particles
by gravity filtration using a filter pipette with a small
cotton plug. Collect the filtrate in another test tube.
Using a Pasteur pipette, mix the solution or suspension to form a
homogeneous sample. Then transfer approximately half of this
solution/suspension into a second test tube. Both samples should
contain approximately 50% of the original total sample.
Part (2) Coupling reaction
q In a 25 OR 50-mL Erlenmeyer flask, place 1.5 mmol
(calculate before proceeding) of one coupling reagent (1- or
2-naphthol, salicylic acid, or 8-anilino-1-naphthalenesulfonic acid ammonium salt, depending on your
assignment).
q Add 1 mL of a 2.5 M aqueous solution of sodium hydroxide
to the Erlenmeyer flask.
q Place the Erlenmeyer flask in an ice-water bath.
q Slowly add half (½) of the diazonium salt suspension
(approximately) prepared in the first step to the Erlenmeyer
flask using a short-stem Pasteur pipette. Agitate the
suspension so you pull the solids into the pipette, and stir the
reaction mixture with a glass rod after each addition. The
color of the solution should change during this period of
reaction.
q After the addition is complete, let the reaction proceed for
about 10 min with occasional stirring.
q After the reaction time has passed, heat the suspension on a
hot plate to a rolling simmer. Add 0.5 g of NaCl and
continue heating for two minutes.
q Cool the Erlenmeyer flask to room temperature. Then cool
it in an ice-water bath.
q Isolate the solid by performing a vacuum filtration using a
Hirsch funnel. Wash the solid with 2 mL of saturated NaCl
solution and let it dry for 5-10 minutes.
Perform a second coupling reaction. Using a different coupling
reagent (assigned to you by your TA), repeat Part (2) with the
rest of your diazonium salt. Both reactions can be performed
simultaneously.
Proceed to “Part (3) Dying a Fiber Strip” on the next page.
Using a Pasteur pipette, mix the solution or suspension to
form a homogeneous sample. Then transfer approximately
half of this solution/suspension into a second test tube. Both
samples should contain approximately 50% of the original
total sample.
Part (2) Coupling reaction
q In a 25 OR 50-mL Erlenmeyer flask, dissolve 2.5 mmol of
one of the four aromatic coupling reagents (1- or 2naphthol,
salicylic
acid,
or
8-anilino-1naphthalenesulfonic acid ammonium salt) in 5 mL of 2.5
M sodium hydroxide solution.
q Place the solution in an ice-water bath.
q Slowly add half (½) the diazonium solution from the
previous step to the Erlenmeyer flask dropwise with
stirring.
q Leave the flask in the ice-water bath for about 10 min and
record any color change.
q Slowly add about 1 mL of concentrated hydrochloric acid
to the mixture until the pH is between 3 and 4.
q Add 0.5 g of NaCl and heat the Erlenmeyer flask on a hotplate until it is boiling.
q Cool the mixture to room temperature and then in an icewater bath.
q Use a small Hirsch funnel to perform a vacuum-filtration
to isolate the solid. (If no solid is formed, the solution/
filtrate can be used to dye the fabrics directly). Wash
the solid with 2-5 mL of water and leave it to dry.
Perform a second coupling reaction. Using a different
coupling reagent (assigned to you by your TA), repeat
Procedure B, Part (2) with the rest of your diazonium salt.
Both reactions can be performed simultaneously.
Proceed to “Part (3) Dying a Fiber Strip” on the next page.
Experimental Procedure (cont.)
Part (3) Dying a fiber strip
q Wear disposable gloves. In a 100-mL beaker, dissolve 50
mg of the azo dye in 20 mL of water. Put a strip of the multifiber (see key to multi-fiber below) in the solution of the azo
dye. Keep the strip immersed and boil the solution for about
5 minutes.
q Remove from heat with a tweezers and rinse the fiber with
tap water.
q Pat the dyed fiber dry with a paper towel and compare the
colors observed as instructed.
If your dyes were isolated as solids, obtain disposable glass vials
and save the material in your drawer (save as much as you can,
and discard the rest).
If your dye was utilized in solution, save approximately 2 mL of
the solution in a disposable vial. Cap and store these inside a
beaker, standing upright to avoid spilling over time. Students in
the ancillary lab (Millis 312) should write their CaseID and
clearly label each vial before turning it in to their TA.
Fabric Strip Content
acetate
cotton
nylon (6,6)
dacron
orlon
wool
Waste Disposal
Discard excess solid dyes in the appropriate waste containers.
Discard solutions in the appropriate waste containers.
Never discard solids in trash bins, nor solutions in the sink.
Colored fabrics will be collected for everyone to see.

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