In the synthesis of aromatic compounds, the sulfonation reaction is a crucial first step that introduces a sulfonic acid group, typically favoring the para position due to higher yields compared to the ortho position. This preference arises from steric and electronic factors that stabilize the para product. Following sulfonation, a nitration reaction is performed using concentrated nitric acid (HNO₃). The nitration will occur at the ortho position because the sulfonic acid group, being an ortho/para director, prevents substitution at the para position where the sulfonic acid is already located.

After the nitration step, the introduction of a nitro group (NO₂) occurs at the ortho position, resulting in a compound with both hydroxyl (OH) and nitro groups. To finalize the synthesis, a desulfonation step is performed using dilute acid and heat, which removes the sulfonic acid group, yielding the desired ortho-substituted product with both the hydroxyl and nitro groups intact.

It is important to note that if nitration were conducted directly on phenol, the major product would indeed be ortho due to hydrogen bonding effects. However, this direct method would yield only about 60% of the ortho product. By employing the three-step pathway involving sulfonation, nitration, and subsequent desulfonation, the yield can be significantly increased to over 90%. This illustrates the advantage of using a blocking group to enhance the overall yield of the desired product, even in cases where ortho substitution might initially seem favored.