Singlet oxygen is a special, excited version of normal molecular oxygen. It can be produced by a special reaction of chlorine with basic hydrogen peroxide.
- In solution, two singlet oxygen molecules crash into each other and release a flash of light which we see as a red glow.
- Outside of this reaction, singlet oxygen is something that’s pretty pervasive in the natural world. Lots of compounds when exposed to light will convert normal oxygen to the singlet form.
Reaction to produce Singlet Oxygen
- Setup a chlorine gas generator. This is what a common setup looks like.
- Prepare a 25% sodium hydroxide solution. Chill hydrogen peroxide and sodium hydroxide to around 0°C.
- Slowly add the hydrogen peroxide to the sodium hydroxide solution. You might notice a slight blueish color.
- Dim the lights. When ready, start the chlorine generator by adding hydrochloric acid to the potassium permanganate. Bubble the produced gas through the freshly prepared solution. A faint, red light will appear.
Singlet Oxygen Reaction and Structure
Singlet oxygen is a quantum state of molecular oxygen. It is produced by the reaction of hypochlorite ions with hydrogen peroxide:
H2O2 + NaOCl → O2(1Δg) + NaCl + H2O
The hypochlorite ion is produced in situ, by bubbling chlorine gas in an aqueous sodium hydroxide solution:
Singlet oxygen refers to one of two singlet electronic excited states. The two singlet states are denoted 1Σ+
g and 1Δg (the preceding superscript “1” indicates a singlet state). The singlet states of oxygen are 158 and 95 kilojoules per mole higher in energy than the triplet ground state of oxygen. Under most common laboratory conditions, the higher energy 1Σ+
g singlet state rapidly converts to the more stable, lower energy 1Δg singlet state. This more stable of the two excited states has its two valence electrons spin-paired in one π* orbital while the second π* orbital is empty. This state is referred to by the title term, singlet oxygen, commonly abbreviated 1O2, to distinguish it from the triplet ground state molecule, 3O2.