Glaser's "Chemistry is in the News"
To Accompany Wade Organic Chemistry 4/e.
Chapter 19. Amines
Nitrates and nitrites are two kinds of salts that are derived from nitric acid and nitrous acid, respectively. They are found everywhere; in water, cosmetics, in meats and even cigarette smoke. Both nitrates and nitrites are used as meat preservatives, as discussed on the The National Food Safety Database Home Page. Nitrites function as an antioxidant in cured meat. They are useful in meat preservation by inhibiting the growth of different bacterium that infect meat, such as Clostridium botulinum, which causes botulism (a deadly form of food poisoning). See the International Food Information Council Home Page for more information. Nitrites are also used by the body to promote blood clotting and heal cuts and burns. Nitrates are used for their antibacterial properties and ability of retention and flavor.
Unfortunately, ingestion of large amounts of nitrites and nitrates are dangerous to human health because they have led to the contribution of nervous disorders, cancer, heart problems, and even death. The man in the article collapsed from eating too many sausages. This is because the nitrates in the sausage lowered his blood pressure by dilating his blood vessels. The third link should be changed so it says "The way this process happens is described on the About.com guide to Heart Disease/Cardiology pages.
Nitrites are also harmful because they are converted to carcinogous nitrosamines when they bond to naturally occurring amines in the body. N-nitrosamines are formed by the addition of a primary or secondary amine to a nitrosonium ion. With primary amines, we actually see the diazotization of an amine reaction, which yields the diazonium salt. (See page 878 in the text.) Nitrosamines are present in many types of substances; in fact they are quite common in other forms of food as well. (See chart below) As an example, in cooked bacon you see dimethylnitrosamines. (See the Phys.com's Nutrition Encyclopedia's Nitrates Page.) As a matter of fact, over 90 percent of nitrosamines have been shown to cause cancer in laboratory animals, but there have been no case of human cancer as a result of them to date.
Ascorbic acid is also used as a meat preservative. Ascorbic acid is the
same thing as vitamin C, look up its structure on the Chemfinder Home Page As you can
see, it is a lactone. Vitamin C is actually beneficial for your heart,
found to lower rates of heart disease and restore normal blood vessel
dilation as reported on the American
Heart Association Home Page. Often a combination of ascorbic acid and
nitrites or nitrates are used as additives in meat. Currently, the USDA
has limited the use of nitrates and nitrites in food preservation to
almost zero. By adding a reducing agent such as ascorbic acid, nitrates
and nitrites are accepted only in small doses.
Pertinent Text References
Chapter 19. Amines.
How are nitrates different from nitrites? (Use the Chemfinder to
compare potassium nitrate with potassium nitrite.)
Answer: Nitrites (NO2-) have one less oxygen bonded to the carbon than nitrates (NO3-).
How do you synthesize nitrites from nitrous acid? How do you
synthesize nitrates from nitric acid?
Answer: To make nitrites and nitrates react a strong base such as NaOH with their respective acids (HNO2 and HNO3). The base deprotonates the acid leaving the nitrite or nitrate and water.
How are nitrosamines formed in your body, and what type of effects do
Answer: When nitrites or nitrates are ingested or inhaled into the body the "free" nitrites/nitrates bond to the amines (proteins) already in the body, forming nitrosamines.
Explain how the over-ingestion of nitrates can cause coronary health
problems. (Hint: See the About.com link.)
Answer: The nitrates act on the wall of the coronary artery by dilating the artery that enters the heart. This causes an increase of blood flow to the heart, which in turn lowers the blood pressure.
Do you think nitrates and nitrites or ascorbic acid are better meat
Answer: Ascorbic acid is a better meat preservative because it actually has health benefits, along with preserving the meat. Ascorbic acid is an antioxidant, forms collagen, and also has been used in prevention and therapy of cancer.
How much exposure to nitrosamines would one person get on a normal
Answer: On a daily basis a normal non-smoker could receive about 0.6 milligrams per person per day. A smoker can increase this by 17 times to 10.2 milligrams per person per day. And considering that the USDA regulates the amount of nitrates and nitrites to almost zero, these are very large numbers.
Table 1. Estimated Exposure to Nitrosamines in the U.S. Source Route of Exposure Exposure cigarette smoker Inhalation 17.00 Scotch Ingestion .03 Cooked bacon Ingestion .17 Beer Ingestion .34 Cosmetics Dermal contact .41 New car interiors Inhalation .50 Cheeses Ingestion .03 a. Adapted from IFT Expert Panel (1987). The exposure data was based on 1981 levels of nitrate consumption. Values for some items may actually be less than listed as significant changes have been made in certain products specifically to lower their nitrate content. b. In micrograms per person per day. Source: Jones, 1992. See URL http://www.foodsafety.org/il/il089.htm