[OrganicZA]

Is the use of chromium trioxide(CrO₃) + H₂O a reasonable replacement for the standard dichromate/sulphuric acid/water to form the oxidising agent chromic acid? 

Has anybody attempted to try this as an alternative method to produce chromic acid to be used in oxidising primary alcohols to aldehydes?

[Hunter2]

It is the same.  The sulfuric is used to set free the chromic acid from its salt. If you have Chromium-VI-oxid then you have at least chromic acid.

[orgopete]

... chromic acid to be used in oxidising primary alcohols to aldehydes?

As I recall, CrO3 is used to produce Jones reagent, so this would be well known. However, chromic acid does not stop at an aldehyde. Aldehydes form hydrates in the presence of water and oxidation of hydrates gives acids. The HCl addition to CrO3 gives chlorochromic acid. This is used to prepare PCC which if used under anhydrous conditions will produce aldehydes on oxidation.

[OrganicZA]

Yes, PCC would be the best option to oxidise the primary alcohol to an aldehyde because the aldehyde hydrate does mot form. However, we are experimenting with chromic acid specifically and in this case I'm asking if it would be possible to exclude sulphuric acid by not preparing the chromic acid through "standard" dichromate/sulphuric/water mix, but rather through CrO₃ and H₂O.

 I understand that if the aldehyde is left exposed to H₂O it will form the aldehyde hydrate and then will be further oxidised by the chromic acid like you say. If I make use of the volatility of the formed aldehyde (in this case ethanal BP ±22°C). I can prevent this from happening to a certain extent by keeping the reaction vessel well above the BP while implementing mechanical stirring, thereby removing acetaldehyde through vapour phase and then condensing it.

[OrganicZA]

Which would you expect to give the more efficient yield of acetaldehyde? Either running dichromate solution(Sodium dichromate/water/sulphuric acid)on to boiling ethanol.Or running the sodium dichromate with water/ ethanol onto boiling dilute sulphuric?Given that a rectification column is employed.Thanks.