To Accompany Wade, Organic Chemistry, 4/e.
Chapter 6. Alkyl Halides: Nucleophilic Substitution and Elimination.
For each of the following questions, please refer to the following article:


Blood substitute May Be Anticipated Break"
by Robert Davis (USA Today, June 20, 2000)
   
   

 

 

 

Did you know that about every 3.7 seconds someone in America has a transfusion of two to three units(pints) of blood? This life-saving substance, the very basis of life, is needed throughout the world, while many non-emergency surgeries are postponed to later dates due to shortage in the blood supply, and while much of the donated blood is found to be tainted by such viruses as HIV, hepatitis, even "mad_cow" disease and isthrown out. Blood typing (A, B, AB, O) causes even more difficulties as to whether or not a person may receive the correct blood type. If you have the universal blood type O you may be out of luck, so to speak, when it comes to receiving other blood types. Or have you ever thought about animals that need surgery? Veterinarians do not usually stockpile different types of animals’ blood. Shortage of blood is a very real threat; by 2030, experts project an annual shortfall of 4 million units in the US. But, what if there were a way to prevent this shortage?

Alliance Pharmaceutical Corp. has developed a new blood substitute called Oxygent, IUPAC name of perfluorooctyl bromide (see the structure using ChemFinder), or Perflubron, which alleviates these problems. This substance is an oxygen carrier and can be used during surgeries safely instead of blood. One of oxygents many benefits is that a person of any blood type can receive oxygent
with no threat of rejection by the body. Oxygen is picked up by hemoglobin (an iron-containing protein) in red blood cells. Whole blood can transport up to 20% volume of oxygen; while fluorinated hydrocarbons, or PFCs such as perfluorotripropylamine, are able to dissolve up to 50% volume of oxygen. Fluorocarbons cannot be used directly in the bloodstream because they are nonpolar and do not mix with water. But, in Oxygent, they have been made as an oxygen carrier by a fluorocarbon-water emulsion with water, salts, and surfactant which are mixed together via high pressure homogenization and heat sterilized, producing small particles suspended in an aqueous solution. Oxygent is injected directly into the blood vessels, where it picks up oxygen from the lungs, transports and releases it to oxygen-depleted tissues. It is also
effective at removing carbon dioxide from the tissues and delivering it to the lungs for expiration. Unlike hemoglobin, Oxygent does not chemically bind the gas molecules, but absorbs and releases them quickly by simple diffusion.

It has been found, for example, that dogs treated with a 25% perfluorotributylamine-water emulsion replacing 70% of their blood can still live a normal life span. Oxygent can be used in various medical circumstances where blood is needed for the transport of oxygen, with little or no known side effects on the human body. Research similar to Alliance’s into patient response and emission of the particles out of the body is currently still being conducted.

Chapter 6.3. Common Uses of Alkyl Halides and following on to Structure and Physical
Properties.
Chapter 6.6. Preparation of Alkyl Halides and following on to Nucleophilic Substitution.
Chapter 25.4. Relating to emulsions

 

Question 1: Use ChemFinder to find out about the structures of the fluorocarbons mentioned
above, and draw the structure of the PFC with the IUPAC name of trans-perfluorodecalin.

                         

Question 2: Is Oxygent a "blood substitute"?

A 2: Oxygent is a "blood substitute" in the sense that it mimics the gas transport function
of the red blood cells, which contain a protein called hemoglobin that is responsible
for delivering oxygen and removing carbon dioxide from the tissues f the body.
There are no products on the market or in development that can substitute for all the
functions of blood provided by the red cells, platelets, white blood cells, and plasma
proteins.

Question 3: What advantages does Oxygent have compared to donor blood?

A 3: UCan be used in patients of any blood type.
UCan be heat_sterilized to prevent bacterial contamination; hemoglobin cannot.
UDoes not transmit viruses or other infectious agents.
UCan be stored for about two years, vs. about 42 days for donor blood.
UDelivers oxygen to tissues more quickly than the hemoglobin in red blood cells.

Question 4: By what mechanism can 1-bromo-heptadecafluorooctane (perflubron) be prepared
Explain or illustrate)

A 4: Doing an Sn2 reaction of octadecafluorooctane with a terminal fluorine as the
leaving group which is replaced by bromine in an aprotic solvent such as acetone or
DMF.

Question 5: How do perfluorochemicals (PFCs) transport oxygen?

A 5: Oxygen molecules are dissolved in PFC particles as they pass, in the blood, through
the lungs. These oxygen_loaded particles travel through the blood to distant
capillaries where tissue oxygen concentrations are low. At that point, oxygen is
exchanged for carbon dioxide molecules. PFCs exchange gases more rapidly and
more completely than do red blood cells because they load and unload gases by
simple diffusion. When the particles return to the lungs, the carbon dioxide is expired
and the PFC particles take on new oxygen molecules.

Chemistry & Society Discussion

Do you think it is ethical to make artificial blood substitutes?

 



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