2. Tollens reagent
• Discovered by German chemist Bernhard Tollens
• Presence of an Aldehyde or alpha-hydroxy ketone functional groups
• It is a colorless, basic, mild oxidizing agent and aqueous
solution containing silver ions coordinated to ammonia, forming
a diaminesilver(I) complex [Ag(NH3)2]+.
• Tollens' reagent itself is reduced to metallic silver.
• Since Tollens’ Reagent has a relatively short shelf life, the
reagent is not commercially sold.
199305 Tollens’ Reagent 09/04/2021
3. Preparation
Step 1: Aqueous silver nitrate is mixed with aqueous sodium hydroxide.
Silver ions in the presence of hydroxide ions come out of solution as a brown precipitate of silver(l) oxide,
Ag2O (s).
Step 2: Aqueous ammonia is added drop-wise until the precipitated silver oxide completely dissolves.
This precipitate dissolves in aqueous ammonia forming the diamine silver (l) ion, [Ag(NH3)2]+
199305 Tollens’ Reagent 09/04/2021
4. Another method of preparation
• Aqueous ammonia can be added directly to silver nitrate solution.
• At first ammonia will induce formation of solid silver oxide
• But with additional ammonia, this solid precipitate dissolve to give a
clear solution of diamine silver (l) coordinated complex, [Ag(NH3)2]+
• Filter this reagent before use to prevent false positive results.
199305 Tollens’ Reagent 09/04/2021
5. Application
1. Qualitative organic analysis
• Tollens' reagent gives a negative test for most ketones, with α-
hydroxy ketone being one exception
(e.g. - hydroxy acetone).
• Tollens' reagent gives a positive test for the presence of an Aldehyde
199305 Tollens’ Reagent 09/04/2021
6. Mechanism for reaction of Tollens'
reagent with aldehydes
https://chemistry.
stackexchange.co
m/questions/139
18/mechanism-
for-reaction-of-
tollens-reagent-
with-aldehydes
199305 09/04/2021
7. • Glucose gives silver mirror test with Tollens' reagent. It is due to
the presence of an aldehydic group (−CHO).
1.https://www.toppr.com/ask/en-
in/question/glucose-gives-silver-mirror-
with-tollens-reagent-it-shows-the/
199305 Tollens’ Reagent 09/04/2021
8. 2. Staining
• Fontana-Masson Stain : It is a silver stain technique
• Detection of melanin, argentaffin and lipofuscin in tissue sections
• By the reduction of Silver nitrate to metallic Silver.
199305 Tollens’ Reagent 09/04/2021
9. 3. Silver mirroring
• Application of silver mirror to glassware
• Inside of insulated vaccum flask, high quality mirror, Telescope
mirrors
https://byjus.com/chemis
try/tollens-test/
199305 Tollens’ Reagent 09/04/2021
10. References
1. Tollens, B. (1882). "Ueber ammon-alkalische Silberlösung als Reagens auf Aldehyd“ - doi:10.1002/cber.18820150243.
2. http://library.med.utah.edu/WebPath/HISTHTML/MANUALS/FONTANA.PDF
3. http://www.chemguide.co.uk/organicprops/carbonyls/oxidation.html
4. Oshitna, K.; Tollens, B. (1901). "Ueber Spectral-reactionen des Methylfurfurols". Ber. Dtsch. Chem. Ges. 34: 1425.
5. Hart, M. (1992). Manual of scientific glassblowing. St. Helens, Merseyside [England]: British Society of Scientific Glassblowers. ISBN 0-9518216-0-1.
6. N. Chitvoranund1; S. Jiemsirilers; D.P. Kashima (2013). "Effects of surface treatments on adhesion of silver film on glass substrate fabricated by
electroless plating". Journal of the Australian Ceramic Society. 49: 62–69.
7. C. Heber D. (February 1911). "Methods of Silvering Mirrors“ - doi:10.1086/122040.
8. Svehla, G.; Vogel, Arthur Anton (1996). Vogel's Qualitative Inorganic Analysis. New York: Longman. ISBN 0-582-21866-7.
9. https://www.toppr.com/ask/en-in/question/glucose-gives-silver-mirror-with-tollens-reagent-it-shows-the/
10. https://byjus.com/chemistry/tollens-test/
11. https://www.chemistrylearner.com/tollens-test.html#:~:text=Tollens'%20test%2C%20also%20known%20as,)%20%5B1%2D4%5D.
12. https://chemistry.stackexchange.com/questions/13918/mechanism-for-reaction-of-tollens-reagent-with-aldehydes
13. https://www.chemistrylearner.com/tollens-test.html#:~:text=Tollens'%20test%2C%20also%20known%20as,)%20%5B1%2D4%5D.
![Tollens reagent
• Discovered by German chemist Bernhard Tollens
• Presence of an Aldehyde or alpha-hydroxy ketone functional groups
• It is a colorless, basic, mild oxidizing agent and aqueous
solution containing silver ions coordinated to ammonia, forming
a diaminesilver(I) complex [Ag(NH3)2]+.
• Tollens' reagent itself is reduced to metallic silver.
• Since Tollens’ Reagent has a relatively short shelf life, the
reagent is not commercially sold.
199305 Tollens’ Reagent 09/04/2021](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)